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From tidal estuaries and back bays to nearshore marine waters, New Jersey’s coastal environments support fisheries, recreation, wildlife, and local economies. Increasingly, however, these valuable ecosystems are vulnerable to a wide range of harmful algal blooms (HABs). While algae are a natural and essential part of aquatic ecosystems, certain environmental conditions can cause some species to grow excessively, leading to ecological damage, public health risks, and economic losses.

Understanding what HABs are, what drives them, and how nature‑based restoration strategies can prevent or mitigate blooms is essential to supporting the long‑term resilience of New Jersey’s coastal environments.


What Are Algae and When Do They Become Harmful?

The term "algae" is ecological rather than taxonomic and encompasses a diverse group of organisms, including eukaryotic algae, such as diatoms and dinoflagellates, and prokaryotic cyanobacteria, commonly referred to as blue‑green algae. Algae are not inherently harmful. In fact, they provide critical ecosystem services, including:

  • Forming the base of aquatic food webs
  • Producing oxygen through photosynthesis
  • Sequestering carbon and contributing to climate regulation
  • Supporting fisheries and overall aquatic health
  • Offering potential applications in biofuel and pharmaceutical development

Phytoplankton are microscopic, free‑floating algae found in freshwater, estuarine, and marine environments. Scientists estimate there are 20,000 to more than 100,000 phytoplankton species, but only a small fraction—roughly 100 to 300 species—are capable of forming toxin‑producing harmful algal blooms. Problems arise when these species proliferate rapidly under favorable conditions. These blooms can become harmful when they produce toxins, deplete oxygen, shade submerged vegetation, or otherwise disrupt ecosystem function.

[gallery link="none" columns="2" ids="19603,19596"] Most toxin‑producing HABs fall into three major groups:
  • Dinoflagellates (often associated with red tides)
  • Diatoms (commonly linked to brown tides)
  • Cyanobacteria (blue‑green algae)

While most harmful algal blooms are caused by phytoplankton, large, fast‑growing macroalgae can also create serious environmental and economic challenges when conditions allow them to proliferate. A well‑known example is Sargassum, a floating seaweed that can form extensive mats across the ocean surface. During periods of rapid growth, these mats can block sunlight from reaching coral reefs and other sensitive habitats. When Sargassum washes ashore in large quantities, it can deter tourism and recreation. As the algae decomposes, it releases hydrogen sulfide gas, producing strong odors that make nearby coastal areas unpleasant to visit. While Sargassum blooms occur most summers along the coast of south Florida, the severity and extent of these events vary considerably from year to year.

HABs can form in freshwater systems, brackish estuaries, and coastal marine waters, and they are particularly dangerous with myriad when they produce toxins that affect humans, pets, livestock, fish, shellfish, and wildlife.

[caption id="attachment_19586" align="aligncenter" width="910"] Source: coastalscience.noaa.gov[/caption]

A Deeper Dive into Marine HABs

Below is a closer look at the dominant types of marine HABs in the region, the organisms responsible, and the environmental conditions that influence their development.

Red Tides (Dinoflagellates)

Common toxin‑producing dinoflagellates include: [gallery link="none" size="full" ids="19587,19588,19589"] [caption id="attachment_19585" align="aligncenter" width="948"] Red tide in summer season, Key West, Florida[/caption]  

Brown Tides (Diatoms and Related Groups)

Brown tides are associated with several diatom genera, such as:

  • Pseudonitzschia sp, known to produce domoic acid which is the marine biotoxin related to amnesic shellfish poisoning (ASP).
  • Pseudo-Nitzschia, cause harm through the production of the neurotoxin domoic acid (DA), which can be transferred to other trophic levels through bioaccumulation.
  • Amphora, can cause ASP in humans and marine mammals, and can accumulate in filter-feeding shellfish, leading to severe health issues.
  • Aureococcus (pelagophyte), a well‑known brown tide organism in mid‑Atlantic estuaries, can cause neurological damage in humans and wildlife.

Environmental Drivers of Red and Brown Tides

These blooms are influenced by a combination of physical, chemical, and climatic factors, including:

  • Increased water temperature and light availability
  • Reduced estuarine flushing or circulation
  • Water column mixing events
  • Elevated salinity
  • Mild winters and dry spring conditions
  • Elevated inorganic nutrients (for many, but not all, species)
  • Inputs of iron and organic nutrients

Green Macroalgal Blooms: Ulva

[caption id="attachment_19593" align="alignright" width="423"] Ulva, commonly known as sea lettuce. Photo Credit: iNaturalist[/caption]

Ulva, commonly known as sea lettuce, is a green macroalga that can form extensive blooms in shallow, nutrient‑rich estuaries. Another common bloomer, Enteromorpha, is now considered genetically equivalent to Ulva. Although Ulva blooms are non‑toxic, they can still cause serious ecological and social impacts:

  • Blooms generate strong odors that reduce recreational value
  • Decomposition consumes oxygen, stressing fish and invertebrates
  • Water clarity declines, further limiting seagrass growth
  • Dense mats can shade and smother seagrass beds
  • Seagrass loss weakens sediment stabilization and reduces habitat quality for many coastal species

Cyanobacteria

[caption id="attachment_19594" align="alignright" width="775"] Cyanobacterial life cycle; details vary among taxa.[/caption] Common bloom‑forming Cyanobacteria genera include:
  • Microcystis
  • Dolichospermum (formerly Anabaena)
  • Aphanizomenon

Cyanotoxins should not be confused with taste‑and‑odor (T&O) compounds. Cyanotoxins are colorless, tasteless, and odorless whereas T&O compounds, such as geosmin and MIB, cause earthy or musty smells. Cyanobacteria can produce T&O compounds without toxins as well as toxins without noticeable odors.

This distinction can complicate detection and public perception of risk.

Environmental Drives of CyanoHABs

HABs are commonly driven by:
  • Warmer water temperatures
  • Reduced flushing and slow‑moving water
  • Stable, stratified water columns
  • Elevated phosphorus concentrations, which increase biomass
  • Increased availability of inorganic nitrogen, which can stimulate toxin production (e.g., microcystins)

Ecological, Human, and Economic Impacts

The impacts of marine and estuarine HABs extend far beyond discolored water.
  • Algal toxins can cause neurological, gastrointestinal, and respiratory symptoms in humans and animals, and in severe cases, death
  • Human fatalities, linked to consuming contaminated shellfish or finfish
  • Fish kills and deaths of birds, sea turtles, and marine mammals associated with toxin exposure
  • Blooms reduce dissolved oxygen and shade seagrasses, stressing or killing aquatic life
  • HABs cause aesthetic and economic losses, including reduced beach access and impacts to commercial fisheries
  • Even non‑toxic blooms can degrade habitat quality and diminish recreational and ecological value
[gallery link="none" ids="9033,1337,11582"]

These HABs, the region's most common, illustrate the wide range of organisms, toxins, and ecological pathways through which algal blooms can affect coastal systems. Although they differ in form, from microscopic phytoplankton to expansive mats of macroalgae, they are often driven by a common set of environmental conditions that favor rapid growth and persistence. Climate change is intensifying many of these drivers. Rising water temperatures, altered precipitation patterns, and longer periods of stratification increasingly create conditions that favor bloom formation. At the same time, human activities continue to increase excess nutrients to coastal waters. Runoff from agricultural lands, chemicals transported by rainfall and irrigation, and discharges from wastewater treatment facilities all introduce nitrogen and phosphorus into rivers, lakes, and estuaries. These nutrients act as fertilizer for algae, accelerating bloom development.

Nutrient‑laden stormwater runoff does not remain localized, rather, it moves downstream through interconnected watersheds, ultimately reaching estuaries and coastal waters where it can contribute to marine blooms. Understanding these linkages between land use, climate, and algae growth is critical to identifying effective strategies for preventing and managing HABs in coastal environments.

[caption id="attachment_13363" align="alignnone" width="1920"] Nutrient sources of HABs - Illustration created by USGS.[/caption]

Nature‑Based and Nearshore Restoration Strategies

A range nature-based nearshore and shoreline restoration and management strategies are increasingly used in coastal systems to help mitigate HABs:
  • Nutrient Remediation in the Watershed: these measures should include sewer upgrades and septic system management as well as stormwater BMPs and green infrastructure, including bioretention basins, rain gardens, and naturalized stormwater features. Helping to reducing nutrients before they reach coastal waters is one of the most effective long‑term HAB mitigation strategies (NJDEP, 2026).
  • Biochar in Watersheds and Aquatic Systems: Biochar is a porous, carbon‑rich material that adsorbs contaminants, especially phosphorus. Its use in waterbodies, particularly nearshore, shallow areas has shown to improve water quality, reduce nutrient availability for algal growth, providing a relatively low‑cost, renewable management option.
  • Nutrient Inactivators in Nearshore, Shallow Sediments: Lanthanum‑modified clays, such as Phoslock, bind with dissolved phosphorus to form a stable mineral that settles into the sediment, preventing it from recycling into the water column. 1lb of phosphorus can generate up to 1,100lbs of wet algae biomass, and 1.1tns of Phoslock can remove 24lbs of phosphorus (SePRO Corporation, 2012).
  • Floating Wetland Islands (FWIs): A single 250‑square‑foot island can function like one acre of natural wetland, improving water quality by assimilating and removing excess nutrients that could fuel algae growth; providing valuable ecological habitat for a variety of beneficial species; helping mitigate wave and wind erosion impacts; providing an aesthetic element; and enhancing biodiversity within open freshwater environments. 1lb of phosphorus can produce 1,100lbs of algae annually; one 250‑square‑foot FWI can remove approximately 10lbs of phosphorus annually, potentially mitigating up to 11,000lbs of algae (Floating Island International, 2011).
[gallery link="none" size="medium" ids="19131,19598,8935"] Additional management approaches, depending on site conditions, may include:   HABs represent a complex and growing challenge in New Jersey’s freshwater, estuarine, and coastal systems. They threaten public health, ecosystems, and coastal economies, but they are not insurmountable. Nutrient control, thoughtful watershed management, and nature‑based restoration strategies are central to preventing, mitigating, and controlling HABs. If you're interested in learning more about our work to identify, assess and mitigate HABs, click here to read about our groundbreaking research project with Friends of Hopewell Valley Open Space to monitor HABs using drone technology, advanced data modeling, and community science across a 73-mile stretch of the Delaware River and 23 associated waterbodies. 

References:

  1. NJDEP, NJ Stormwater Best Management Practices Manual, 2026
  2. SePRO Corporation, An Overview of Phoslock and Use in Aquatic Environments, 2012
  3. Floating Island International, Phosphorus Reduction with Passive Floating Treatment Wetlands, 2011
[post_title] => Harmful Algal Blooms in New Jersey’s Coastal Waters: Causes, Impacts and Nature‑Based Solutions [post_excerpt] => [post_status] => publish [comment_status] => open [ping_status] => open [post_password] => [post_name] => marine-habs [to_ping] => [pinged] => [post_modified] => 2026-05-04 16:09:27 [post_modified_gmt] => 2026-05-04 16:09:27 [post_content_filtered] => [post_parent] => 0 [guid] => https://princetonhydro.com/?p=19571 [menu_order] => 0 [post_type] => post [post_mime_type] => [comment_count] => 0 [filter] => raw ) [1] => WP_Post Object ( [ID] => 19087 [post_author] => 1 [post_date] => 2026-03-13 14:32:04 [post_date_gmt] => 2026-03-13 14:32:04 [post_content] =>

Nutrient-driven water quality impairments, particularly harmful algal blooms (HABs), continue to challenge lake managers, municipalities, and watershed organizations across the Northeast. Excess phosphorus and nitrogen can rapidly degrade ecological conditions, limit recreational use, impact sources of potable water, and increase management costs, often despite the implementation of conventional best management practices. As a result, there is growing interest in tools that can complement or augment existing approaches and address nutrients in more targeted ways.

Biochar has emerged as one such tool. While it is best known as a soil amendment, its physical, chemical, and biological properties have prompted increasing use in aquatic systems as a means of improving water quality. Over the past five years, Princeton Hydro has applied biochar in a range of lakes, ponds, streams, and stormwater-related settings across Pennsylvania, New Jersey, and New York. These field applications, supported by monitoring, have provided important insight into when biochar is most effective, where its limitations lie, and why observed improvements in water quality are not always explained by phosphorus removal alone.

[gallery link="none" size="medium" ids="9215,19122,9225"]

What Is Biochar and Why Use It in Waterbodies?

Biochar is a carbon-rich, charcoal-like material produced through pyrolysis, a process in which organic biomass is heated in a low-oxygen environment. The resulting material has a highly porous structure and extensive surface area, properties that make it effective at adsorbing nutrients such as phosphorus and nitrogen (Joseph et al., 2021). Because excess nutrients are a primary driver of eutrophication and HABs, biochar has emerged as a promising amendment for aquatic systems and stormwater best management practices (BMPs).

In aquatic applications, biochar is typically installed in permeable sleeves (aka socks) or incorporated into stormwater treatment practices to intercept nutrient-rich water before it enters lakes or ponds. Used biochar can also be repurposed as a soil amendment, adding to its appeal as a sustainable, circular material.

[gallery link="none" columns="2" size="medium" ids="19134,9226"]
Aquatic Ecologist Katie Walston-Frederick (right) leads a biochar sleeve filling session. Katie and her team members wear full protective equipment when handling biochar due to the fine, carbon-based nature of the material.

Lessons Learned from Five Years of Field Applications

Through approximately half a dozen monitored projects implemented since 2020, several consistent patterns have emerged.

Standing Waters Show the Strongest Response: Biochar has proven most effective in low-flow or standing water environments such as ponds and stormwater basins. In these systems, Princeton Hydro has documented total phosphorus (TP) removal rates as high as 80%, with soluble reactive phosphorus (SRP) reductions approaching 97% in some stormwater ponds (Princeton Hydro, Lake Hopatcong Report, 2022). The extended contact time between water and biochar in these settings appears to be a key driver of performance.

Flow and Contact Time Matter: In streams and fast-moving stormwater infrastructure, nutrient removal rates tend to be lower, with phosphorus reductions typically closer to 50%. While still meaningful, these reduced efficiencies are largely attributable to limited contact time. Simply put, the shorter the interaction between water and biochar, the fewer opportunities there are for adsorption and other removal processes to occur.

Enhancement to Conventional Stormwater BMPs: Biochar can be particularly effective when paired with stormwater BMPs that primarily rely on sedimentation. Traditional practices often excel at removing particulate-bound phosphorus but are less effective at capturing dissolved forms of phosphorus—the fraction most readily utilized by algae. Incorporating biochar into these systems can enhance removal of dissolved phosphorus, improving overall treatment performance.

Streams Present Physical Challenges: Installing biochar in stream environments presents practical challenges. Even with careful anchoring, large storm events, including remnants of hurricanes, can dislodge biochar sleeves, transporting them downstream or onto streambanks. These risks must be considered during design and often limit the suitability of biochar for higher energy systems.

Chemistry Alone Does Not Tell the Whole Story: At very high pH levels, phosphorus adsorption onto biochar can become less predictable, sometimes exhibiting a “decoupling” between measured phosphorus sorption and observed water quality improvements. Monitoring data from multiple projects indicate that reductions in chlorophyll-a, cyanobacteria abundance, and overall bloom severity cannot always be explained by phosphorus removal alone.


Beyond Adsorption: The Role of Biology

The disconnect between measured nutrient sorption and improved water quality suggests that additional mechanisms are at work. Increasingly, evidence points toward biological processes occurring within and around biochar installations.

Biochar is known to favor the growth and proliferation of heterotrophic bacteria (Moore et al., 2023). These microbial communities may contribute to water quality improvements in the following ways:

  • Assimilating nutrients like nitrogen and phosphorus and locking them into microbial biomass, making those nutrients less available to fuel harmful algal blooms
  • Supporting a natural food web process in which bacteria are eaten by small organisms, gradually moving nutrients up the aquatic food chain rather than leaving them available for algae
  • Encouraging the growth of bacteria that can help break down cyanobacteria cells and the toxins they produce, such as microcystins. Some types of bacteria are even capable of breaking down microcystins, which are the toxins produced by certain HABs, and using them as a food source (Moore et al., 2023).

This emerging science mirrors what Princeton Hydro has observed in the field: water quality can improve in ways that chemical measurements alone do not fully explain, suggesting that biological processes may be playing an important supporting role.


Biochar in Practice: Case Studies from the Field

Since 2020, Princeton Hydro has applied biochar across a range of aquatic and stormwater settings, tailoring each installation to site-specific conditions and management goals. Together, these projects demonstrate biochar’s versatility and its ability to integrate into holistic watershed and lake management strategies, often working best when paired with other nature-based and engineered solutions.

1. Duke Farms, NJ - Integrating Biochar into Long-term Lake Management

At Duke Farms, a 2,700-acre estate in New Jersey, Princeton Hydro has supported lake and wetland management efforts for more than two decades. Biochar was recently introduced as an additional tool within an established, science-based nutrient management program. By placing biochar in low-flow areas where contact time could be maximized, phosphorus removal was enhanced and improvements in water clarity were observed. This effort highlights how biochar can be layered into long-term management strategies alongside floating wetland islands and other nature-based solutions.

[caption id="attachment_18916" align="aligncenter" width="1227"] Biochar socks and a floating wetland island installed in Mermaid Pool.[/caption]
2. Harvey’s Lake, PA - Stormwater Nutrient Reduction

Harvey’s Lake, the largest natural lake in Pennsylvania, has long faced challenges associated with nutrient loading and recurring HABs. As part of a broader stormwater management effort, Princeton Hydro incorporated biochar into select stormwater BMPs to reduce phosphorus before it entered the lake. Installed within targeted stormwater conveyance and treatment features, the biochar helped achieve measurable reductions in dissolved phosphorus, complementing other watershed-scale measures such as vegetated buffers and wetland enhancements. The spent biochar, having captured phosphorus and nitrogen from runoff, was then repurposed as a soil amendment to enrich a 500-square-foot pollinator garden. This repurposing effort served a dual purpose: demonstrating a closed-loop approach to managing excess nutrients while also creating a community-oriented space that supports local biodiversity.

[gallery link="none" columns="2" size="large" ids="17611,17612"]

3. Regional Stormwater Projects - Scaling a Targeted Approach

Across multiple stormwater projects in New Jersey and Pennsylvania, biochar has been installed in detention basins, rain gardens, and other stormwater treatment devices. These applications were designed to target dissolved phosphorus, a nutrient form that conventional BMPs can struggle to remove. In several cases, biochar was paired with other nutrient control measures such as floating wetland islands to further improve nutrient capture. Collectively, these projects illustrate how biochar can be adapted and scaled to address local water quality challenges across diverse settings.

[gallery columns="2" link="none" size="medium" ids="19127,19128"]

4. Lake Hopatcong, NJ - Biochar at the State's Largest Lake

At Lake Hopatcong, New Jersey’s largest lake, biochar was deployed as part of a comprehensive, multi-pronged strategy to reduce nutrient concentrations and mitigate HABs. Biochar was installed in permeable flotation bags and placed at targeted shoreline and inlet locations where nutrient loading is most pronounced, including several stormwater inlets and outlets around the lake. Funded through the NJDEP Freshwater HABs Prevention & Management Grant Program and implemented in partnership with the Lake Hopatcong Commission and the Lake Hopatcong Foundation, these installations complemented other in-lake management measures such as floating wetland islands.

[gallery columns="2" link="none" size="medium" ids="9141,9143"]

5. Central Park, NYC - Biochar within a Holistic Urban Lake Management Strategy

In Manhattan's Central Park, Princeton Hydro supported the Central Park Conservancy in developing and implementing a long-term management strategy for the park's network of lakes and ponds, where harmful algal blooms driven by excess nutrients were a persistent concern. As part of a broader, phased approach to improve water quality, biochar was incorporated as a nutrient reduction tool and will be incorporated alongside other measures such as floating wetland islands, aeration and circulation, and stormwater treatment techniques. Used in targeted locations, biochar helped support efforts to reduce nutrient loading and mitigate cyanobacteria blooms within these highly visible urban waterbodies.

[gallery link="none" size="medium" ids="19132,19131,1122"]

Across these projects, biochar installations have been associated with measurable reductions in total and dissolved phosphorus, decreases in chlorophyll‑a concentrations, and lower cyanobacteria cell counts. While performance has varied by site, the strongest and most consistent results have occurred in enclosed or low‑flow environments where contact time is maximized and physical disturbance is minimized. When thoughtfully designed and integrated with other BMPs, these case studies show how biochar can contribute meaningfully to broader efforts to reduce nutrient loads and improve overall water quality.


Looking Ahead & Learning More

Biochar is not a one-size-fits-all solution. Reviewing site-specific water quality data is essential to determine whether biochar is an appropriate standalone treatment or should be combined with complementary approaches. Ongoing and future research is focused on better quantifying the relative contributions of chemical adsorption and biological activity associated with biochar. Current studies, including collaborative efforts with academic partners, aim to document pollutant removal capacity, characterize microbial communities, and evaluate biochar’s potential role in degrading cyanobacteria and cyanotoxins. As these processes continue to be studied and further understood in the water quality context, biochar may become an increasingly valuable component of integrated, science-based watershed management strategies.

Want to learn more? Check out our Youtube tutorial filmed on lake in Hemlock Farms, PA: [embed]https://www.youtube.com/watch?v=XHswfXKCCTQ[/embed] [post_title] => Harnessing Biochar to Improve Water Quality: Lessons from the Field [post_excerpt] => [post_status] => publish [comment_status] => open [ping_status] => open [post_password] => [post_name] => harnessing-biochar-to-improve-water-quality-lessons-from-the-field [to_ping] => [pinged] => [post_modified] => 2026-03-13 14:45:47 [post_modified_gmt] => 2026-03-13 14:45:47 [post_content_filtered] => [post_parent] => 0 [guid] => https://princetonhydro.com/?p=19087 [menu_order] => 0 [post_type] => post [post_mime_type] => [comment_count] => 0 [filter] => raw ) [2] => WP_Post Object ( [ID] => 19285 [post_author] => 1 [post_date] => 2026-03-12 14:33:49 [post_date_gmt] => 2026-03-12 14:33:49 [post_content] =>

Dr. Fred Lubnow, Princeton Hydro's Senior Technical Director of Ecological Services, and Jenn Rogers, Executive Director of Friends of Hopewell Valley Open Space (FoHVOS), were recently featured on the Native Plants, Healthy Planet podcast to discuss the collaborative, first‑of‑its‑kind initiative to monitor Harmful Algal Blooms (HABs) in the Delaware River Watershed using drones, spatial analysis, and community science.

The Delaware River is a lifeline for more than 14 million people, a refuge for wildlife, and a defining natural feature of the region. In recent years, HABs, once confined mostly to lakes and ponds, have expanded into streams and rivers and appearing in colder months. Understanding why this shift is happening, and how to predict it, is essential for protecting water quality, public health, and ecological resilience within the Delaware River watershed and watersheds nationwide.

The podcast, hosted by Fran Chismar and Tom Knezick of Pinelands Nursey, highlights the urgency of addressing HABs and the innovative, cross‑sector partnership driving this work forward. Listen now: Harmful Algal Blooms with Dr. Fred Lubnow and Jenn Rogers.


Stewardship and Community Leadership from FoHVOS

Jenn Rogers, Executive Director of FoHVOS, brings two decades of conservation leadership to the partnership. Her background spans naturalist education, ecological stewardship, and the development of large-scale restoration and public engagement programs. During her fourteen years with the Mercer County Park Commission, she helped establish both the Environmental Education and Stewardship Departments and oversaw the care of more than ten thousand acres of parkland.

Jenn has spent her career building programs that connect people to the landscapes around them. Her commitment to community-driven conservation make her a key partner in a project that relies on both scientific rigor and public participation. Her perspective highlights how land use, watershed health, and community stewardship are deeply interconnected.

Expertise Shaping the Future of HAB Research

Dr. Fred Lubnow serves as Princeton Hydro’s Senior Technical Director of Ecological Services and brings more than 30 years of experience in limnology, watershed restoration, and community and ecosystem ecology. His career has focused on understanding how freshwater systems respond to nutrient loading, hydrologic change, and long-term environmental pressures. He has designed and led numerous lake and watershed restoration projects, developed USEPA Nine-Element and TMDL-driven watershed plans, and created field-based cyanobacteria and cyanotoxin monitoring programs that are now used across the region.

Fred’s expertise in the taxonomy, ecology, and management of algae, particularly cyanobacteria, has made him a leading voice in the study of HABs. He currently serves on New Jersey’s HABs Advisory Team, where he helps interpret water quality data and advises on mitigation strategies. His scientific leadership guides the technical design and implementation of the Delaware River HAB monitoring initiative.


A Collaborative Approach to Understanding HABs

Now entering its second year, the Delaware River HAB monitoring initiative is expanding both its scientific scope and its community engagement efforts. Building on the foundation established in 2025, the project team is conducting multi‑season drone flights, enhanced satellite‑based surveys, and targeted on‑the‑water sampling along 73 miles of the Delaware River and 24 connected waterbodies. These efforts are designed to strengthen the project’s ability to detect and forecast HABs under a wide range of seasonal and environmental conditions.

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Year two also introduces several tools and activities intended to support broader participation and more efficient data collection. This includes the launch of a new ArcSurvey123 mobile data platform to support real‑time volunteer water quality submissions, as well as expanded training opportunities for community members interested in assisting with field sampling. Data collected through these efforts will contribute to the development of advanced algorithms capable of forecasting HAB occurrence at multiple spatial scales.

Funded by the National Fish and Wildlife Foundation's (NFWF) Delaware Watershed Conservation Fund (DWCF), in partnership with U.S. Fish & Wildlife Service, the project continues to be supported by a diverse network of partners across New Jersey and Pennsylvania, including The City University of New York's (CUNY) New York City College of Technology (City Tech), Trenton Water Works, Mercer County Park Commission, The College of New Jersey, Aqua-PA, Philadelphia Water Department, Bucks County Conservation District, Turner Designs, and US Army Corps of Engineers - Philadelphia District's Blue Marsh Lake. Together, these organizations contribute technical expertise, watershed knowledge, and crucial on‑the‑ground support. This collaborative approach remains central to the initiative’s success and long‑term objective: establishing a scalable HAB‑forecasting framework that can ultimately be applied to additional watersheds across the United States.

For a deeper look at the research, partnerships, and shared commitment behind this initiative, listen to the full Native Plants, Healthy Planet podcast presented by Pinelands Nursery. Click here to learn more about the Pinelands Nursery and explore the full library of Native Plants, Healthy Planet podcasts. If you're interested in getting involved in the Delaware River HAB research initiative, the program is currently seeking volunteers for water sampling along the Delaware and select waterbodies. Contact FoHVOS Conservation Biologist Kaitlin Muccio at: kmuccio@fohvos.org for more details.

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Friends of Hopewell Valley Open Space (FoHVOS), in partnership with Princeton Hydro, has launched a groundbreaking initiative, “Monitoring Harmful Algal Blooms (HABs) in the Delaware River Watershed Using Drones and Spatial Analysis,” to improve understanding and forecasting of HABs throughout the Delaware River Watershed. Funded by the National Fish and Wildlife Foundation (NFWF), in partnership with the U.S. Fish & Wildlife Service, through the Delaware Watershed Conservation Fund (DWCF), the project leverages drone technology and advanced data modeling to identify environmental conditions that contribute to HAB formation and aims to develop tools and methodologies for early detection and management.

For this innovative research project, FoHVOS, a 501(c)3 and accredited Land Trust located in Hopewell Township, NJ, has teamed with Princeton Hydro. Princeton Hydro conceptualized and designed the initiative and is leading the technical implementation, including field survey design, drone operations, data analysis, and volunteer training.

“The Delaware River is central to Hopewell Valley’s identity. It shapes our way of life, supplies drinking water to 14.2 million people, shelters wildlife like the endangered Atlantic sturgeon, and offers abundant outdoor recreation,” said Jennifer Rogers, Executive Director of FoHVOS. “HABs were once confined to ponds and lakes, but since 2018, they’ve appeared in colder months and spread to streams and rivers. Though land trusts traditionally focus on land, HABs show how land use directly affects water. These blooms often stem from excess nitrogen and phosphorus washed into waterways during storms. Protecting water means restoring land. Our partnership with Princeton Hydro aligns perfectly with our mission. Together, we’re working to better understand and safeguard the Delaware River and its tributaries in both NJ and PA.”

HABs, caused by nuisance growth of cyanobacteria, can have detrimental effects on water quality and are a growing environmental concern nationwide. These blooms deplete oxygen levels, release toxins, and disrupt ecosystems, potentially posing serious risks to drinking water supplies and the health of wildlife, pets, humans, and local economies. Despite advances in environmental monitoring, predicting when and where HABs will occur remains a challenge due to the complex interplay of nutrient loading, temperature, and hydrologic conditions that can lead to rapid bloom proliferation.

To address these challenges, this newly launched initiative integrates drone-based remote sensing, field sampling, and spatial data analysis to collect and interpret detailed environmental data over a two-year period. The study spans multiple monitoring sites along a 73-mile stretch of the Delaware River in New Jersey and Pennsylvania, focusing on near-shore sections and 23 associated waterbodies. The first survey event began in August 2025.

 

Drones equipped with multispectral imaging systems capture high-resolution spatial data that is then integrated with digital platforms to link remote-sensing with the drone data and on-the-water collected data. The field-based water quality measurements are being collected by a team of trained community volunteers who are using phycocyanin fluorometer meters to measure concentrations of the photosynthetic pigment phycocyanin, which is produced primarily by cyanobacteria. Volunteers enter the data into a customized ArcGIS mobile-friendly survey. These combined datasets will be used to develop and validate predictive algorithms for both planktonic and benthic HABs under varying seasonal and hydrologic conditions.

The following photos depict the RGB (Visual) and corresponding Thermal image from the monitoring flights over Spring Lake in New Jersey:

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“This research project represents a major step forward in how we study and manage harmful algal blooms at the watershed scale,” said Dr. Fred Lubnow, Project Lead and Senior Technical Director of Ecological Services at Princeton Hydro. “By integrating satellite data, drone imagery, and on-the-water sampling, we’re developing predictive tools that will enable us take a proactive approach to mitigate HABs, improve response time, and better support our ecosystem health.”

Project partners include New York City College of Technology – The City University of New York, which donated the drone and is supporting remote sensing and data integration; Trenton Water Works, Mercer County Park Commission, and The College of New Jersey which are providing monitoring sites and contributing volunteers for water quality data collection in New Jersey; Aqua-PA and the Philadelphia Water Department, which are providing monitoring sites and volunteers to collect watershed data in Pennsylvania; the Bucks County Conservation District, which is coordinating volunteer data collection; and Turner Designs, whose advanced phycocyanin sensors are being used to calibrate and validate drone-based monitoring data.

In the photos below, volunteers are being trained by Princeton Hydro staff on how to use phycocyanin fluorometers and Secchi disks to gather water quality data and log their findings.

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This $1M project is funded through a $488,400 NFWF DWCF grant as part of the NFWF’s Research, Monitoring, & Evaluation Grant category and $513,700 in matching funds from project partners. This grant category aims to support high-performing science that is inclusive, adaptive, and innovative, with the potential to transform the Delaware River Watershed’s future through improved conservation, restoration, and public engagement.

Once complete, the project will produce a comprehensive report summarizing methods, analyses, and data-driven recommendations for practical, low-cost HAB monitoring and mitigation strategies that can be replicated across the Delaware River Watershed and beyond. Crucially, the report will identify tributaries and sources contributing to riverine HABs, enabling targeted restoration of the most affected lands and waters. Data collection will continue through Fall 2025, resume in Spring/Summer 2026, and culminate in a final report expected in 2027.

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FoHVOS is a 501(c)3 nonprofit land trust dedicated to conserving the natural resources of the Hopewell Valley region and beyond. Through land preservation, ecological restoration, community engagement, and science-driven initiatives, FoHVOS works to protect and enhance open spaces for future generations. Learn more at www.fohvos.org.

Princeton Hydro is committed to improving our ecosystems, quality of life, and communities for the better. The firm was formed in 1998 with the specific mission of providing integrated ecological and engineering consulting services. Offering expertise in natural resource management, water resources engineering, geotechnical design and investigation, and regulatory compliance, their staff provide a full suite of environmental services throughout the Northeast for the public and private sectors. Project Lead, Dr. Fred Lubnow, is an expert in HAB management and has worked with dozens of lake associations and government agencies to restore lakes, manage watersheds, reduce pollutant loading, address invasive aquatic plants, and mitigate nuisance HABs. To learn more about Princeton Hydro's work to mitigate harmful algal blooms, go here.

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Nestled in Luzerne County, Pennsylvania, Harveys Lake spans 622 acres and is the largest natural lake by volume in the Commonwealth. Beyond its scenic beauty and popularity as a recreational destination, the lake plays a critical ecological role in the region.

Harveys Lake forms the headwaters of Harveys Creek, which flows into the Susquehanna River and ultimately the Chesapeake Bay. As such, it is part of the greater Susquehanna River Valley and contributes to the health of the Chesapeake Bay watershed. The lake and its outflow are designated High Quality – Cold-Water Fisheries, supporting sensitive aquatic life, providing vital cold-water habitat, and contributing to regional biodiversity.

Given its ecological significance and its connection to regional waterways, efforts to manage stormwater and reduce nutrient pollution in the Harveys Lake watershed are more than just local improvements, they are integral to protecting downstream water quality all the way to the Chesapeake Bay.

In 2022, building on decades of water quality initiatives, the Borough of Harveys Lake launched a forward-thinking pilot project to enhance stormwater treatment using innovative nutrient-filtering technologies. Supported by funding from the National Fish and Wildlife Foundation (NFWF) Chesapeake Bay Small Watershed Grant Program and designed and implemented in partnership with Princeton Hydro, this project explores the use of biochar and EutroSORB® filtration media to capture dissolved nutrients, an important step toward improving water quality and meeting regulatory goals.

This blog explores the local history of water management at Harveys Lake, the science behind this novel pilot approach, and the broader implications for watershed protection across the region.


Historical Management of Harveys Lake

Once a remote, wooded landscape, the Harveys Lake area was settled in the early 19th century and gradually developed into a hub for timbering and milling. By the late 1800s, the lake was regularly stocked with game fish, and with the arrival of the railroad in 1887, it quickly became a popular summer destination. The shoreline soon featured hotels, restaurants, and even an amusement park.

As the community flourished, the lake's natural systems began to show signs of strain. Like many waterbodies across the country, Harveys Lake faced growing water quality challenges driven by stormwater runoff, nutrient pollution, and a lack of formal environmental protections. By the 1960s, declining water clarity and seasonal algal blooms began to impact recreation, contributing to the lake’s gradual transition from a bustling public getaway to a primarily residential community.

[caption id="attachment_12423" align="aligncenter" width="896"] Harveys Lake, Luzerne County, PA in February 2023 (photo by Jason Miller)[/caption]  

A significant shift occurred following the passage of the U.S. Environmental Protection Agency’s Clean Water Act of 1972. Harveys Lake established a municipal sewer authority, and construction began on a utility line around the lake's perimeter to reduce point-source pollution. Still, algae blooms persisted throughout the 1980s, fueled by nonpoint sources such as stormwater runoff, lawn fertilizers, and waterfowl droppings.

In 1994, a Phase I Diagnostic Feasibility Study was conducted that formally identified Harveys Lake as impaired due to recurring algal blooms linked to elevated nutrient levels. Following this study, a Total Maximum Daily Load (TMDL) was established, and management efforts were initiated to meet long-term water quality goals.

Since 2003, the Harveys Lake watershed has undergone extensive stormwater management efforts, including the installation of numerous manufactured treatment devices (MTDs) to reduce pollutant loading. Most of these MTDs are nutrient separating baffle boxes (NSBBs), chosen due to the watershed’s steep slopes, dense residential development, and shallow bedrock. The first NSBB, pictured below, was installed at Hemlock Gardens:

 

In 2009, the Borough of Harvey’s Lake worked with Princeton Hydro to develop a Stormwater Implementation Plan that laid the foundation for future restoration efforts. Over the following years, the Borough of Harveys Lake, supported by state and regional grants, implemented 34 stormwater best management practices (BMPs) and installed four floating wetland islands throughout the watershed. Volunteers install native plants in one of the FWIs installed in Harveys Lake. Photo by: Mark Moran, The Citizen’s Voice.

These projects were strategically designed to reduce nutrient loading, enhance water quality, and move the lake closer to achieving its TMDL targets. Click here to read more about these efforts.


Innovative Solutions for Stormwater Nutrient Reduction

While NSBB stormwater BMPs are highly effective at capturing sediments and associated pollutants, they are limited in their ability to remove dissolved nutrients, particularly nitrogen and phosphorus. This is evident in the Harveys Lake Watershed, where NSBBs remove approximately 70% of total suspended solids (such as sediment and plant debris), 35% of total phosphorus, and 0% of total nitrogen. To address this gap and improve overall nutrient removal efficiency, the Borough of Harveys Lake received funding from the NFWF Chesapeake Bay Small Watershed Grant Program to augment existing MTD stormwater BMPs using new filter technologies.

Partnered with Princeton Hydro for design, implementation, and technical support, the Borough launched a unique pilot project involving the installation of biochar and EutroSORB® (manufactured by SePRO Corporation) to evaluate the effectiveness of these two innovative materials in removing dissolved phosphorus and total nitrogen from stormwater runoff before it reaches Harveys Lake.

Biochar, a carbon-rich material derived from plant biomass, is valued for its high surface area and nutrient-adsorption capacity. EutroSORB® is a manufactured media specifically engineered to bind and retain dissolved phosphorus with demonstrated effectiveness in aquatic systems.

Filter socks filled with either biochar or EutroSORB® were installed at key stormwater outfalls and stream inlets that drain directly to the lake. At four NSBB sites, the socks were secured beneath manhole covers using a rope-and-carabiner system designed for easy, seasonal replacement. Each sock weighs approximately 50–60 pounds when saturated and was carefully positioned to avoid dislodgement or blockage of outlet pipes during high-flow events.

At the Hemlock Gardens site, which features a larger, multi-tray baffle box, twelve filter socks were installed across two horizontal trays to maximize contact time between stormwater and the filter media.

By integrating these innovative filter techniques into the existing BMP infrastructure, the Borough of Harveys Lake is taking a proactive, science-based approach to nutrient reduction and long-term water quality improvement.


Measuring Success: Sampling, Monitoring, & Key Findings

Princeton Hydro implemented a comprehensive water quality monitoring program in the Harveys Lake watershed to assess the real-world performance of the biochar and EutroSORB® filtration systems under varying hydrologic conditions, with a particular focus on dissolved nutrients that contribute to eutrophication.

Monitoring Set-Up

Six stormwater monitoring stations were established at locations where biochar or EutroSORB® were deployed within NSBBs or stream inlets. Each site included paired upstream (pre-treatment) and downstream (post-treatment) sampling points to capture the nutrient concentrations entering and exiting the filtration media.

Stormwater sampling was conducted during six separate rainfall events between March and April 2025. At each location, during storm flow conditions, discrete grab samples were collected via a portable polyethylene sampling pole and analyzed for key water quality parameters.

Data Analysis & Pollutant Load Modeling

Beyond concentration-based comparisons, Princeton Hydro used empirical monitoring data to model pollutant loads upgradient and downgradient of the filtration media. These load estimates provide insights into pollutant removal effectiveness on a mass basis, with a focus on:

  • Total Nitrogen (TN),
  • Total Phosphorus (TP),
  • Total Suspended Solids (TSS), and
  • Soluble Reactive Phosphorus (SRP).

Emphasis was placed on SRP—the biologically available form of phosphorus most readily assimilated by algae and a key driver of harmful algal blooms and eutrophication. Because phosphorus is the target pollutant in Harveys Lake’s TMDL, SRP reduction serves as a critical indicator of the filtration media’s performance and its potential role in long-term water quality management strategies.

Key Findings

Overall, the study revealed variable but promising results across media types and installation locations:

  • SRP: Reductions were more pronounced in the EutroSORB® dataset, with 50-83% of NSBB samples and 67% of stream samples showing improvement. Biochar performed well in stream applications, achieving SRP reductions in 83% of samples, and moderately in NSBBs, with 33-67% showing positive results.
  • TN: Reductions were most evident in EutroSORB®-treated NSBBs, with 67-100% of samples showing a net decrease in concentrations.
  • TP: Removal was most effective in NSBBs utilizing EutroSORB®, where 67% of samples showed a net reduction, with values ranging from -14% to -70%. Biochar-treated NSBBs demonstrated more modest results, with 33-50% of samples showing TP reductions.

These early findings suggest that both EutroSORB® and biochar hold promise as cost-effective tools for reducing soluble phosphorus in stormwater runoff. Additionally, observed differences in removal efficiency, based on installation context (NSBB vs. stream), filter media volume, and site-specific hydrologic conditions, underscore the importance of continued monitoring and system refinement.


Engaging the Community & Enriching the Landscape

As part of the project’s commitment to long-term sustainability and public education, a native pollinator garden was established near the Harveys Lake Department of Public Works garage, adjacent to the Little League fields.

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After the final sampling in April 2025, the nutrient-saturated biochar and EutroSORB® socks were removed from the stormwater treatment systems. The spent biochar, having captured phosphorus and nitrogen from runoff, was repurposed as a soil amendment to enrich a 500-square-foot planting area. This repurposing effort served a dual purpose: demonstrating a closed-loop approach to managing excess nutrients while also creating a community-oriented space that supports local biodiversity.

The Harveys Lake Environmental Advisory Council volunteered to help plant the garden, installing 450 native plant plugs across nine species including Foxglove Beardtongue, Clustered Mountain Mint, Blue Wild Indigo, and Common Yarrow to attract pollinators such as butterflies, bees, and songbirds.

Designed by Princeton Hydro, the pollinator garden serves as both an ecological asset and an educational tool. Its prominent location next to the ballfields encourages community engagement, and an interpretive sign on-site helps visitors understand the garden’s purpose and its connection to local water quality initiatives. The sign features a QR code linking to an interactive ArcGIS StoryMap, developed by Princeton Hydro, which explores the broader context of the project. It draws connections between nutrient management efforts in Harveys Lake and similar challenges facing the entire Chesapeake Bay watershed, emphasizing how local actions contribute to regional water quality improvements. To support public outreach, the StoryMap was also shared on the Borough’s website, making this educational resource widely accessible to the community.

Click here to learn more about and explore the StoryMap.

It is important to note that while this project illustrates a successful example of biochar reuse, all reuse applications must be assessed on a case-by-case basis. For example, biochar exposed to hazardous pollutants is not suitable for soil use. In this case, the biochar had only been used to absorb excess nutrients, making it appropriate for the garden setting.


A Scalable, Shareable Solution

Supported by the U.S. Environmental Protection Agency and the NFWF’s Chesapeake Bay Stewardship Fund, which promotes community-based conservation strategies to protect and restore Chesapeake Bay’s natural resources, this project was designed with scalability in mind. A core objective was to evaluate whether these filtration media could be more broadly implemented throughout the Chesapeake Bay watershed as a low-cost, community-integrated strategy for achieving water quality goals.

Through continued innovation and shared learning, small-scale efforts like this can drive large-scale impact, proving that effective water quality solutions don’t have to be costly or complex. The Harveys Lake model offers a replicable framework that communities across the region can adopt and adapt, empowering local action that contributes meaningfully to the restoration and resilience of Chesapeake Bay.

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By Dr. Fred Lubnow, Senior Technical Director of Ecological Services

As we reflect on the winter of 2023-2024, it's evident that New Jersey experienced another unusually mild season, mirroring the winter of 2022-2023. Notably, Lake Hopatcong, located in Sussex and Morris Counties, remained virtually ice-free throughout the winter, with only a brief period of minor ice formation in early January. This pattern was not isolated to Lake Hopatcong; many lakes across the state and the broader Mid-Atlantic region exhibited similar ice-free conditions. Such conditions can lead to increased algal and plant growth earlier in the year.

Adding to this, from January to early June 2024, 15 of New Jersey's 21 counties recorded precipitation levels 26% to 50% higher than their long-term averages. The remaining six counties, predominantly in the southern part of the state, had precipitation increases of 11% to 25% above their long-term normals. This heightened precipitation is significant as it can transport nutrients, most notably phosphorus and nitrogen, into water bodies, potentially fueling the growth of algae.

Compounding these factors, long-range climate models and trends suggest that the summer of 2024 could rank among the hottest on record. The combination of a mild winter, increased precipitation, and anticipated high summer temperatures sets the stage for conditions similar to those experienced in 2019, a year marked by widespread harmful algal blooms (HABs) in numerous lakes.

HABs, characterized by rapid overgrowths of cyanobacteria, present serious challenges to water quality and aquatic ecosystems. Cyanobacteria, or blue-green algae, naturally occur in aquatic environments but can proliferate rapidly under warm, nutrient-rich conditions. These blooms pose risks to human health, wildlife, aquatic species, local economies, and the overall ecological balance. The interplay between climate change and HABs is undeniable: rising temperatures and altered precipitation patterns foster conditions that exacerbate bloom occurrences.

Given these circumstances, it is crucial for lake managers and water utilities to adopt proactive measures. Early and consistent sampling efforts can detect cyanobacteria and akinetes, dormant spores that contribute to bloom formation. Additionally, reducing nutrient inputs, particularly phosphorus, into waterways is essential to prevent HABs. Princeton Hydro strongly recommends that lake managers, water utilities, and concerned community members closely monitor their lakes, reservoirs, and riverways to stay as proactive as possible in managing these valuable resources.

By raising awareness, fostering collaboration, and implementing effective strategies, we can work towards safeguarding the health and sustainability of our freshwater ecosystems. Together, we can address the challenges posed by HABs and protect the integrity of our water bodies. For more information about HABs, click here.


Dr. Fred Lubnow, Princeton Hydro’s Senior Technical Director, Ecological Services, is an expert in aquatic and watershed management, restoration ecology, community and ecosystem ecology, and the use of benthic macroinvertebrate and fish in-stream bioassessment protocols. Dr. Lubnow has managed hundreds of lake projects and provides technical expertise for a variety of lake and watershed restoration projects.

His experience in lake and reservoir restoration includes the design and implementation of dredging, aeration, chemical control of nuisance species, nutrient inactivation (i.e. alum) and biomanipulation. His experience in watershed restoration includes the design and implementation of structural Best Management Practices (BMPs), the development of Total Maximum Daily Load (TMDL) pollutant budgets, and the design, implementation and analysis of watershed-based monitoring programs.

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Did you know that New York State is home to a rich tapestry of natural waterbodies, including over 7,600 freshwater lakes, ponds, and reservoirs? Our team recently journeyed to Lake George, New York, to participate in the 41st annual conference of the New York State Federation of Lake Associations (NYSFOLA).

This year’s conference, themed “It Takes a Community to Protect a Watershed,” brought together environmental experts, lake management professionals, students, recreation enthusiasts, watershed advocates, and lake community members to advance the best available information and techniques for protecting and restoring New York’s watersheds. The two-day program featured a diverse exhibitor hall, networking events, a silent auction, a student poster session and a variety of presentations and workshops that combined science, policy, practical applications, and tangible resources.

Princeton Hydro, a proud sponsor of the conference, led two presentations during the “Climate Resilience and Your Lake" segment of the educational program:

Michael Hartshorne, Director of Aquatics, delivered an insightful presentation titled "Impacts of Climate Change on Lake Ecology," which delved into the significant role of climate change in shaping lake ecosystems. During the session, Michael highlighted key factors such as rising water temperatures, heightened frequency and severity of rainfall, depletion of dissolved oxygen, fluctuating patterns of algal blooms, and the migration of invasive species due to changing latitudinal conditions. His presentation underscored the necessity for evolving approaches to lake management in response to these profound ecological shifts.

[gallery link="none" size="medium" columns="2" ids="14984,14982"] Download the complete presentation now!

Dr. Fred Lubnow, Senior Technical Director of Ecological Services, presented "A Survey of the Ecology of Select Lakes and Ponds in Central Park, NYC," which provided an insightful overview of Princeton Hydro's water quality and ecological monitoring efforts conducted across lakes and ponds of Central Park from 2020 to 2023 for the Central Park Conservancy. These assessments revealed elevated nutrient levels driving planktonic algae, filamentous mat algae and in some cases high densities of aquatic plants, prompting the Central Park Conservancy and Princeton Hydro to collaborate on a tailored Management Plan. Fred’s presentation spotlighted the distinct ecological profiles of key sites, addressed the impact of cyanobacteria on both ecological dynamics and recreational usage, and provided practical management methods and techniques.

[gallery link="none" size="medium" columns="2" ids="14961,14983"] Download the complete presentation now!

Additional educational session topics included, Environmental Justice and New York Lakes, Community Leadership for Healthy Lakes in New York State, and iMap Invasive Species Workshop. Click here to view the complete agenda.

Founded in 1983, NYSFOLA is a not-for-profit coalition of lake associations, individuals, and corporate members dedicated to the protection and restoration of New York lakes. Princeton Hydro is the industry leader in lake restoration and watershed management. We have conducted diagnostic studies and have developed management and restoration plans for over 300+ lakes and watersheds throughout the country. Our long-standing partnership with NYSFOLA as a corporate member, annual conference sponsor, and active participant highlights our unwavering commitment to collaborative initiatives aimed at safeguarding our water resources. To learn more about our lake and natural resource management services and how we're contributing to a healthier environment, click here. 

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When we hear about harmful algal bloom (HAB) outbreaks, like those recently spotted in New Jersey, the first thoughts that come to mind usually involve discolored waters, environmental disruption, closed beaches, and potential human health hazards. Yet, a crucial aspect that often escapes the spotlight is the impact of these blooms on animals, including pets, wildlife, and livestock.

As HABs proliferate due to factors like excess nutrients and warming waters, the impacts ripple across a wide spectrum of living things, encompassing everything from aquatic species to humans to our animal companions, working animals, and livestock. Animals are most at risk because they may bathe/swim in affected water, drink contaminated water, or ingest it when cleaning algae from fur/hair coat, and the symptoms of HABs toxicity can go unnoticed for a period of time.

The U.S. Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) released a new factsheet that specifically provides an array of information and techniques to safeguard livestock from the dangers of HABs. 

In this blog, we provide links to the USDA NRCS's newly released informational resources, shed light on the often-unseen consequences of HABs, and outline steps to protect the four-legged members of our agricultural communities.


Deciphering HABs

HABs are rapid, large overgrowths of cyanobacteria. Cyanobacteria, also known as blue-green algae, aren’t actually algae, they are prokaryotes, single-celled aquatic organisms that are closely related to bacteria and can photosynthesize like algae. These microorganisms are a natural part of aquatic ecosystems, but, under the right conditions (e.g., heavy rains followed by hot, sunny days), these organisms can rapidly increase to form HABs. Climate change is leading to more frequent, more intense rainstorms that drive run-off pollutants into waterways, coupled with more hot days that increase the water temperature, creating the ideal environment for HABs to proliforate.  In recent years, HABs have begun to appear in more places, earlier in the summer.

[caption id="attachment_13363" align="aligncenter" width="1230"]Nutrient sources of HABs. Illustration created by USGS. Nutrient sources of HABs. Illustration created by USGS. Click image to enlarge.[/caption]  

HABs can cause significant water quality issues in lakes and ponds, often forming a visible and sometimes odorous scum on the surface of the water. They can produce toxins that are incredibly harmful (even deadly) to humans, aquatic organisms, and animals, including livestock.


Mitigating Livestock Exposure to HABs

The health impacts and symptoms can vary depending on the size and type of animal, how an animal is exposed to the cyanotoxin, how long they were exposed, which type of toxin was present, and how much toxin was present.

Symptoms of cyanotoxin exposure in animals includes: vomiting, profuse salivation, fatigue, unsteady gait, labored breathing, convulsions, and liver malfunction. When animals bathe or swim in waters with even low concentrations of cyanotoxins, it may cause skin rashes, ear/throat infections, and gastrointestinal distress. In severe cases, especially when contaminated water is ingested, HAB poisoning can prove fatal.

When HABs are present in a waterbody that is accessible to and utilized by livestock, it's important to immediately restrict access to the contaminated water. If a potential exposure to cyanotoxins has occurred, NRCS recommends:

  1. Washing animals with clean water and monitoring for symptoms of exposure to cyanotoxins.
  2. Isolating any animals exhibiting symptoms and seeking veterinary care as soon as possible.
  3. Providing animals with an alternative source of fresh, safe drinking water.
  4. Contacting the appropriate state agency for sampling and testing guidance to test the water source for HABs and cyanotoxins. Please note: It is not safe for landowners to sample the water themselves without proper personal protective equipment and procedures.
  5. Visiting the CDC website for further information, or contacting your state/county health department.

In its newly released fact sheet, NRCS also provides a number of ideas for segregating livestock from tainted waters, reducing the risk of livestock exposure to HABs, and providing alternate water sources, including:

  1. Installing protective fencing (Conservation Practice 382)
  2. Constructing purposeful ponds (Conservation Practice 378)
  3. Implementing access control measures (Conservation Practice 472)
  4. Establishing reliable water wells (Conservation Practice 642)
  5. Designing effective watering facilities (Conservation Practice 614)
To download the USDA NRCS fact sheet, click below:

To minimize the risk of future HABs, it's important to stay informed, routinely monitor waterbodies, take actions to reduce harmful effects, and adopt conservation practices that prevent nutrient loading to waterbodies.

Princeton Hydro is regionally recognized for its HABs expertise, having provided management recommendations and services for 100+ lakes and ponds in the Northeast, including Lake Hopatcong, New Jersey’s largest lake. To learn more about our lake management and HABs prevention services, click here. For additional HABs resources from the USDA NRCS, click here.

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We are pleased to announce that the Lake Hopatcong Foundation (LHF) received the prestigious New Jersey Governor's Environmental Excellence Award in the Environmental Education category for its innovative floating classroom program.

The LHF's floating classroom - a custom-built 40-foot education vessel, named ‘Study Hull’ - gives students an interactive, hands-on education experience to explore Lake Hopatcong, learn about freshwater ecology, and discuss how to protect the watershed.

During its maiden voyage field trip, which was held on May 21 2018, fourth-graders from Nixon Elementary and Kennedy Elementary schools utilized the boat’s laboratory instruments to study water hydrology, temperatures, plankton, and dissolved oxygen levels.Princeton Hydro helped the LHF design a teaching curriculum on water quality, and members of our team trained the LHF staff and volunteers on the curriculum and demonstrated various water quality monitoring techniques that could be conducted with the students.

The floating classroom is equipped with laboratory instruments on which the students can study water hydrology, temperatures, plankton, and dissolved oxygen levels. Course instructors assist students in performing tests and experiments designed to help them learn about the general health of the lake. They also discuss the impacts that stormwater runoff and nonpoint source pollutants have on the lake, and how they can protect the lake’s water quality and be good stewards of the water.

The Governor’s Environmental Excellence Awards are given each year to individuals and organizations that demonstrate commitment and leadership on a variety of environmental issues, including environmental justice, climate change, sustainability, education, and protection of natural resources. The Governor's Award is a testament to the hard work and dedication of the LHF and the educators who run the floating classroom. It is also a testament to the value of experiential learning and the importance of connecting young people to the natural world.

“It’s really important to get kids interested in science at an early age and teach them about their surrounding environment – where their drinking water comes from, how it could possibly get polluted, the impacts that pollution then has on the lake’s ecosystem, and what steps can be made to protect the lake’s water quality," said Princeton Hydro Senior Aquatic Ecologist Chris L. Mikolajczyk, CLM, one of the team members responsible for developing the floating classroom curriculum. "We are proud to partner with the Lake Hopatcong Foundation and extend to them our sincerest congratulations on receiving the Governor's Environmental Excellence Award for their innovative and unique floating classroom initiative. Well deserved!”

The 23rd Annual Governor’s Environmental Excellence Awards were announced virtually by the Commissioner of Environmental Protection Shawn M. LaTourette. The video recording is available on DEP’s YouTube channel.

[embed]https://youtu.be/yayIyRj9r3w?si=5h6Nb0lwwI9hmRIG[/embed]

Lake Hopatcong, New Jersey's largest lake, has one of the longest, continuous, long-term ecological databases in New Jersey; almost 30 years of consistently collected water quality data. The data is crucial in assessing the overall health of the lake and proactively guiding its management, identifying and addressing emerging threats, documenting project success, and confirming compliance with New Jersey State Water Quality standards.

The LHF works to foster a vibrant and healthy Lake Hopatcong and its surrounding community through a variety of programs and initiatives in the areas of environment, education, community and historical preservation, public safety, recreation, and arts and culture. The LHF and Princeton Hydro are longtime partners with history dating back to 1983. Princeton Hydro’s recent work for Lake Hopatcong includes the implementation of green infrastructure stormwater management measures, installation of floating wetland islands to improve water quality, and invasive aquatic plant species management programs, community educational training, and surveys. To learn more about LHF, check out our Client Spotlight blog.

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The NJ Department of Environmental Protection (NJDEP) hosted its 3rd Annual Harmful Algal Bloom (HAB) Summit! The all-day, virtual seminar included expert presentations and facilitated open-forum discussions related to HAB science, monitoring, response, management, treatment and communication.

Approximately 220 people from around the country participated in the virtual summit, which was free and open to the public. The audience of stakeholders included government officials (local, state, federal); lake and other environmental commissions; watershed associations; environmental nonprofits; businesses; academics; lake management and HAB treatment experts; and folks interested in protecting their community lakes.

Participants heard presentations about “Keeping Your Pets Safe from HABs,” “The Benefit of Riparian Buffers;” and “Stormwater Management and the Use of Green Infrastructure.” Additionally, two members of the NJDEP HAB Expert Team - Dr. Fred Lubnow Director and Dr. Meiyin Wu - gave a presentation on best management practices to prevent, mitigate, and/or control HABs. The 10-person expert team was established as part of Governor Phil Murphy’s plan to enhance scientific expertise around water quality management and bolster the State’s response to HABs.

The Governor’s HABs Initiative was launched in 2019 after lakes throughout NJ (and the entire Continental U.S.) suffered from HAB outbreaks, which caused local and county health agencies to close off all beaches and issue advisories. These unprecedented conditions had significant negative impacts on lake-related ecological, recreational, and economic resources. The Governor’s initiative designated $13 million in funding to local communities for HABs reduction/prevention; established the aforementioned HABs expert team; and coordinated annual HABs summits in order to encourage continued community education and discussion.

If you were unable to attend the 2022 HAB Summit, NJDEP has made the complete morning and afternoon sessions available online:

Watch the Morning Session: 

[embed]https://www.youtube.com/watch?v=3KzeIP4FY60[/embed]

Watch the Afternoon Session: 

[embed]https://www.youtube.com/watch?v=vSfJXhcaPCo[/embed]  

The NJDEP Division of Water Monitoring and Standards has an entire website dedicated to HABs. Click here to access educational fact sheets, stay informed on HAB alerts and advisories, and report a HAB sighting.

For more information about HABs, watch a live interview with Dr. Fred Lubnow on Jersey Matters during which he discusses what steps should be taken to prevent HABs:

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From tidal estuaries and back bays to nearshore marine waters, New Jersey’s coastal environments support fisheries, recreation, wildlife, and local economies. Increasingly, however, these valuable ecosystems are vulnerable to a wide range of harmful algal blooms (HABs). While algae are a natural and essential part of aquatic ecosystems, certain environmental conditions can cause some species to grow excessively, leading to ecological damage, public health risks, and economic losses.

Understanding what HABs are, what drives them, and how nature‑based restoration strategies can prevent or mitigate blooms is essential to supporting the long‑term resilience of New Jersey’s coastal environments.


What Are Algae and When Do They Become Harmful?

The term "algae" is ecological rather than taxonomic and encompasses a diverse group of organisms, including eukaryotic algae, such as diatoms and dinoflagellates, and prokaryotic cyanobacteria, commonly referred to as blue‑green algae. Algae are not inherently harmful. In fact, they provide critical ecosystem services, including:

  • Forming the base of aquatic food webs
  • Producing oxygen through photosynthesis
  • Sequestering carbon and contributing to climate regulation
  • Supporting fisheries and overall aquatic health
  • Offering potential applications in biofuel and pharmaceutical development

Phytoplankton are microscopic, free‑floating algae found in freshwater, estuarine, and marine environments. Scientists estimate there are 20,000 to more than 100,000 phytoplankton species, but only a small fraction—roughly 100 to 300 species—are capable of forming toxin‑producing harmful algal blooms. Problems arise when these species proliferate rapidly under favorable conditions. These blooms can become harmful when they produce toxins, deplete oxygen, shade submerged vegetation, or otherwise disrupt ecosystem function.

[gallery link="none" columns="2" ids="19603,19596"] Most toxin‑producing HABs fall into three major groups:
  • Dinoflagellates (often associated with red tides)
  • Diatoms (commonly linked to brown tides)
  • Cyanobacteria (blue‑green algae)

While most harmful algal blooms are caused by phytoplankton, large, fast‑growing macroalgae can also create serious environmental and economic challenges when conditions allow them to proliferate. A well‑known example is Sargassum, a floating seaweed that can form extensive mats across the ocean surface. During periods of rapid growth, these mats can block sunlight from reaching coral reefs and other sensitive habitats. When Sargassum washes ashore in large quantities, it can deter tourism and recreation. As the algae decomposes, it releases hydrogen sulfide gas, producing strong odors that make nearby coastal areas unpleasant to visit. While Sargassum blooms occur most summers along the coast of south Florida, the severity and extent of these events vary considerably from year to year.

HABs can form in freshwater systems, brackish estuaries, and coastal marine waters, and they are particularly dangerous with myriad when they produce toxins that affect humans, pets, livestock, fish, shellfish, and wildlife.

[caption id="attachment_19586" align="aligncenter" width="910"] Source: coastalscience.noaa.gov[/caption]

A Deeper Dive into Marine HABs

Below is a closer look at the dominant types of marine HABs in the region, the organisms responsible, and the environmental conditions that influence their development.

Red Tides (Dinoflagellates)

Common toxin‑producing dinoflagellates include: [gallery link="none" size="full" ids="19587,19588,19589"] [caption id="attachment_19585" align="aligncenter" width="948"] Red tide in summer season, Key West, Florida[/caption]  

Brown Tides (Diatoms and Related Groups)

Brown tides are associated with several diatom genera, such as:

  • Pseudonitzschia sp, known to produce domoic acid which is the marine biotoxin related to amnesic shellfish poisoning (ASP).
  • Pseudo-Nitzschia, cause harm through the production of the neurotoxin domoic acid (DA), which can be transferred to other trophic levels through bioaccumulation.
  • Amphora, can cause ASP in humans and marine mammals, and can accumulate in filter-feeding shellfish, leading to severe health issues.
  • Aureococcus (pelagophyte), a well‑known brown tide organism in mid‑Atlantic estuaries, can cause neurological damage in humans and wildlife.

Environmental Drivers of Red and Brown Tides

These blooms are influenced by a combination of physical, chemical, and climatic factors, including:

  • Increased water temperature and light availability
  • Reduced estuarine flushing or circulation
  • Water column mixing events
  • Elevated salinity
  • Mild winters and dry spring conditions
  • Elevated inorganic nutrients (for many, but not all, species)
  • Inputs of iron and organic nutrients

Green Macroalgal Blooms: Ulva

[caption id="attachment_19593" align="alignright" width="423"] Ulva, commonly known as sea lettuce. Photo Credit: iNaturalist[/caption]

Ulva, commonly known as sea lettuce, is a green macroalga that can form extensive blooms in shallow, nutrient‑rich estuaries. Another common bloomer, Enteromorpha, is now considered genetically equivalent to Ulva. Although Ulva blooms are non‑toxic, they can still cause serious ecological and social impacts:

  • Blooms generate strong odors that reduce recreational value
  • Decomposition consumes oxygen, stressing fish and invertebrates
  • Water clarity declines, further limiting seagrass growth
  • Dense mats can shade and smother seagrass beds
  • Seagrass loss weakens sediment stabilization and reduces habitat quality for many coastal species

Cyanobacteria

[caption id="attachment_19594" align="alignright" width="775"] Cyanobacterial life cycle; details vary among taxa.[/caption] Common bloom‑forming Cyanobacteria genera include:
  • Microcystis
  • Dolichospermum (formerly Anabaena)
  • Aphanizomenon

Cyanotoxins should not be confused with taste‑and‑odor (T&O) compounds. Cyanotoxins are colorless, tasteless, and odorless whereas T&O compounds, such as geosmin and MIB, cause earthy or musty smells. Cyanobacteria can produce T&O compounds without toxins as well as toxins without noticeable odors.

This distinction can complicate detection and public perception of risk.

Environmental Drives of CyanoHABs

HABs are commonly driven by:
  • Warmer water temperatures
  • Reduced flushing and slow‑moving water
  • Stable, stratified water columns
  • Elevated phosphorus concentrations, which increase biomass
  • Increased availability of inorganic nitrogen, which can stimulate toxin production (e.g., microcystins)

Ecological, Human, and Economic Impacts

The impacts of marine and estuarine HABs extend far beyond discolored water.
  • Algal toxins can cause neurological, gastrointestinal, and respiratory symptoms in humans and animals, and in severe cases, death
  • Human fatalities, linked to consuming contaminated shellfish or finfish
  • Fish kills and deaths of birds, sea turtles, and marine mammals associated with toxin exposure
  • Blooms reduce dissolved oxygen and shade seagrasses, stressing or killing aquatic life
  • HABs cause aesthetic and economic losses, including reduced beach access and impacts to commercial fisheries
  • Even non‑toxic blooms can degrade habitat quality and diminish recreational and ecological value
[gallery link="none" ids="9033,1337,11582"]

These HABs, the region's most common, illustrate the wide range of organisms, toxins, and ecological pathways through which algal blooms can affect coastal systems. Although they differ in form, from microscopic phytoplankton to expansive mats of macroalgae, they are often driven by a common set of environmental conditions that favor rapid growth and persistence. Climate change is intensifying many of these drivers. Rising water temperatures, altered precipitation patterns, and longer periods of stratification increasingly create conditions that favor bloom formation. At the same time, human activities continue to increase excess nutrients to coastal waters. Runoff from agricultural lands, chemicals transported by rainfall and irrigation, and discharges from wastewater treatment facilities all introduce nitrogen and phosphorus into rivers, lakes, and estuaries. These nutrients act as fertilizer for algae, accelerating bloom development.

Nutrient‑laden stormwater runoff does not remain localized, rather, it moves downstream through interconnected watersheds, ultimately reaching estuaries and coastal waters where it can contribute to marine blooms. Understanding these linkages between land use, climate, and algae growth is critical to identifying effective strategies for preventing and managing HABs in coastal environments.

[caption id="attachment_13363" align="alignnone" width="1920"] Nutrient sources of HABs - Illustration created by USGS.[/caption]

Nature‑Based and Nearshore Restoration Strategies

A range nature-based nearshore and shoreline restoration and management strategies are increasingly used in coastal systems to help mitigate HABs:
  • Nutrient Remediation in the Watershed: these measures should include sewer upgrades and septic system management as well as stormwater BMPs and green infrastructure, including bioretention basins, rain gardens, and naturalized stormwater features. Helping to reducing nutrients before they reach coastal waters is one of the most effective long‑term HAB mitigation strategies (NJDEP, 2026).
  • Biochar in Watersheds and Aquatic Systems: Biochar is a porous, carbon‑rich material that adsorbs contaminants, especially phosphorus. Its use in waterbodies, particularly nearshore, shallow areas has shown to improve water quality, reduce nutrient availability for algal growth, providing a relatively low‑cost, renewable management option.
  • Nutrient Inactivators in Nearshore, Shallow Sediments: Lanthanum‑modified clays, such as Phoslock, bind with dissolved phosphorus to form a stable mineral that settles into the sediment, preventing it from recycling into the water column. 1lb of phosphorus can generate up to 1,100lbs of wet algae biomass, and 1.1tns of Phoslock can remove 24lbs of phosphorus (SePRO Corporation, 2012).
  • Floating Wetland Islands (FWIs): A single 250‑square‑foot island can function like one acre of natural wetland, improving water quality by assimilating and removing excess nutrients that could fuel algae growth; providing valuable ecological habitat for a variety of beneficial species; helping mitigate wave and wind erosion impacts; providing an aesthetic element; and enhancing biodiversity within open freshwater environments. 1lb of phosphorus can produce 1,100lbs of algae annually; one 250‑square‑foot FWI can remove approximately 10lbs of phosphorus annually, potentially mitigating up to 11,000lbs of algae (Floating Island International, 2011).
[gallery link="none" size="medium" ids="19131,19598,8935"] Additional management approaches, depending on site conditions, may include:   HABs represent a complex and growing challenge in New Jersey’s freshwater, estuarine, and coastal systems. They threaten public health, ecosystems, and coastal economies, but they are not insurmountable. Nutrient control, thoughtful watershed management, and nature‑based restoration strategies are central to preventing, mitigating, and controlling HABs. If you're interested in learning more about our work to identify, assess and mitigate HABs, click here to read about our groundbreaking research project with Friends of Hopewell Valley Open Space to monitor HABs using drone technology, advanced data modeling, and community science across a 73-mile stretch of the Delaware River and 23 associated waterbodies. 

References:

  1. NJDEP, NJ Stormwater Best Management Practices Manual, 2026
  2. SePRO Corporation, An Overview of Phoslock and Use in Aquatic Environments, 2012
  3. Floating Island International, Phosphorus Reduction with Passive Floating Treatment Wetlands, 2011
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