New Jersey American Water – Harmful Algal Bloom Monitoring

During the summer of 2022, a harmful algal bloom (HAB) occurred in the waters of the Millstone River. This HAB was in close proximity to the intakes of the New Jersey American Water (NJAW) potable water treatment plant located at the confluence of the Millstone and South Branch Raritan Rivers. NJAW took a proactive approach to monitor their intakes for the presence of this HAB, and also established monitoring locations on both rivers upstream of the plant, in addition to the nearby D&R Canal, which also serves as a water source to the treatment plant.

On each sampling date, Princeton Hydro conducted both in-situ and discrete water quality monitoring. The in-situ data was collected at the three (3) pre-determined NJAW collection points: the D&R Canal intake (A), the Millstone River intake (B), and the Raritan River intake (C), as sampled in 2022 and 2023. At these locations, dissolved oxygen (DO), temperature, pH, specific conductivity, and meter-based chlorophyll a and phycocyanin were measured in profile (from surface to bottom at pre-determined intervals) using a multi-probe water quality meter. In addition, clarity was measured and reported as Secchi disk transparency.

Notes were recorded relative to the occurrence and density of any submerged aquatic vegetation (SAV) observed. Additionally, a discrete sample was collected at each location for phytoplankton species identification and enumeration, with emphasis placed on cyanobacteria presence and concentrations. Lastly, a service report detailing the collected data, phytoplankton species and counts, as well as field observations and photographs, was sent to the client 24–48 business hours after each monitoring event.

This monitoring occurred monthly from April to November, unless NJAW dictated an increased frequency as a result of a HAB or suspected HAB in the river system, which did occur in both 2023 and 2024.

Additionally, following the 2024 monitoring events, and using data from 2022 and 2023, Princeton Hydro performed a linear correlation analysis on the meter-based phycocyanin data so that a correlation equation between cyanobacteria cell counts and phycocyanin concentrations could be specifically developed for the Millstone River plant.