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Harmful algal blooms reported in Rockland County lakes

The DEC urges the public to report sightings and track active blooms through its website.

Diane Caruso

May 29, 2026, 5:00 PM

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Harmful algal blooms have appeared this week in Rockland Lake and Sebago Lake in Rockland County, prompting reminders from state experts about reporting them.

Brian Duffy, of the New York State Department of Environmental Conservation (DEC), described blooms as “Green streaky, spilled paint appearance, pea soup appearance, sometimes chunks, sometimes green globs.”

Duffy said harmful algal blooms, often called HABs, become more common as the weather warms.

“This is when they're ramping up - hot, dry conditions. As temperatures increase, as they're doing now, that's when we see blooms occurring all across the state," Duffy says.

He noted they may be more prevalent during late summer months.

The DEC urges the public to report sightings and track active blooms through its website. While research continues into long‑term mitigation tools, Duffy says there are currently limited options for treating blooms once they appear. Lakes themselves typically remain open, but swimming areas can be closed if blooms are detected.

News 12 couldn't find any blooms at either lake on Friday while people were out enjoying the water.

Experts say high phosphorus levels are a major driver of harmful algal blooms. Jen Zunino‑Smith, of the Cornell Cooperative Extension of Rockland, explained that phosphorus is an emerging contaminant.

"That means we're not hearing a lot about it now, but we will start to hear more and more about it," Zunino‑Smith says.

She noted that everyday activities, such as cutting grass or washing cars, can contribute to phosphorus runoff when materials flow into storm drains. New York state law prohibits the use of fertilizers containing phosphorus unless specific conditions are met.

Anna Hickey, also with the Cornell Cooperative Extension of Rockland, said residents can check fertilizer labels to ensure compliance.

“There's always a ratio on the front of the fertilizer bag and the middle number represents phosphorus, and you want that number to be zero," she says.

The DEC says they have a research grant program to address HAB challenges.

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