Community Science Institute reports rising HAB reports on Keuka Lake, narrows 2025 sampling to priority public-supply sites

Grayson Scheidemanno, executive director of the Community Science Institute, told the Seneca County Board of Supervisors that the group’s volunteer monitoring on Keuka Lake and its tributaries recorded a record number of harmful algal bloom (HAB) reports in 2024 and that CSI will change its 2025 sampling protocol to focus laboratory analyses on priority locations identified by county health departments.

CSI’s monitoring program relies on trained volunteers who visually patrol shoreline zones and report blooms; the organization’s state-certified lab analyzes samples for cyanobacteria, chlorophyll a and microcystin toxin. Scheidemanno said CSI received 127 HAB reports in 2024 — the most since the program began in 2018 — and that more than half of tested blooms each year exceed New York’s contact-recreation microcystin guidance of 4 micrograms per liter in some samples.

"We will continue visual monitoring and reporting of HABs as usual," Scheidemanno said. "However, we will only be collecting samples for analysis in priority locations that have been identified by the county departments of health." He listed the priority sites in Seneca County as five public water supplies (sites not named in the presentation). The change is intended to concentrate lab work where public-health risk is greatest and to reduce volunteer burden so shoreline coverage can increase.

Why it matters: CSI emphasized that citizen-collected, laboratory-analyzed data are regulatory-quality when processed under a quality-assurance plan and analyzed in a state-certified lab. That data is intended to inform state reporting (the DEC integrated reports and HAB tracking) and local public-health responses.

Supporting details and findings: Scheidemanno presented median total-phosphorus comparisons for Seneca County tributaries and noted that Williamson and Burrows creeks have higher median phosphorus than a draft DEC guidance value for the ecoregion, while Canoga, Johnsons and Sheldrake creeks were typically lower. He cautioned that median values do not capture episodic spikes: "Johnsons Creek, for example, will often show much higher total phosphorus concentrations than what you can see by just looking at the median." Scheidemanno urged supervisors to consult CSI’s public database for site-level and event-level data.

On HABs, CSI’s 2024 analyses showed blooms in the northern end of Keuka Lake tended to be more toxic and to contain more Microcystis, the cyanobacteria genus that commonly produces microcystin, than blooms in the southern end. Scheidemanno said the program upgraded its HAB database in late 2024 and early 2025 to make maps and filtering tools faster and more usable.

Questions and context: Board members and attendees asked about public-supply vulnerability, whether boiling treated or untreated lake water would reduce toxin risk (Scheidemanno: boiling kills cells but can release intracellular toxin and is not an effective treatment for microcystin), and how CSI’s data are used by state agencies (Scheidemanno: CSI submits quality-assured data to DEC’s two-year integrated reporting cycle and reports HABs to DEC and county health departments for the statewide HABs map).

Scheidemanno thanked Seneca County and the Seneca County Health Department for funding support of CSI’s synoptic stream and lake monitoring and HAB programs and said the funding helps maintain long-term datasets.

Ending: Board members did not vote on policy during the presentation; supervisors and members of the public repeatedly described water quality and HABs as a county priority and thanked CSI for the data and monitoring support. Scheidemanno said CSI will implement the 2025 sampling prioritization and will continue to provide data to DEC and county health departments.