Lake Ronkonkoma is suffering its first blue-green algae bloom of the year, a Suffolk County health department spokeswoman said on Wednesday.
So everyone and their pets must avoid the Island’s largest and deepest lake, and all swimming and wading is barred, the Suffolk Department of Health Services said in a statement.
The presence of the cyanobacteria bloom, which also harms marine life, was confirmed by Stony Brook University, it said.
The algae, which can look like scum or streaks of paint, feeds on nitrogen from fertilizers and wastewater from homes.
Those who touch the algae or get it on their clothing should immediately wash it off and seek help if they experience nausea, vomiting or diarrhea; skin, eye or throat irritation; or allergic reactions or breathing difficulties, the county said.
Algae blooms are more common in the summer, because of higher temperatures.
The beach at Lake Ronkonkoma is closed and will not open for swimming until late June, a spokeswoman for the Town of Islip said by email.