The number of Suffolk County lakes affected by blue green algae has more than tripled in three years, raising concerns about the safety of local swimming holes, environmental activists said Monday.

Leaders from the Long Island Clean Water Partnership, a consortium of local environmental groups, cited new data from the state Department of Environmental Conservation that they said showed algal blooms are occurring in more Suffolk lakes and lasting longer.

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Adrienne Esposito, executive director of Citizens Campaign for the Environment in Farmingdale, said the number of contaminated Suffolk County lakes has grown from one in 2012 to 16 last year. That number had been five in 2013, she said.

Lake Ronkonkoma, where Monday’s announcement was made, had its first blue green algae bloom last year, Esposito said. She said Suffolk leads New York State in the number of contaminated fresh water lakes.

“It’s absolutely alarming,” Esposito said in an interview. “It illustrates that the problem of toxic blue green algae is getting worse and worse, and that it is a direct threat to public health.”

Algal blooms, caused by untreated sewage discharges, can cause health issues such as liver failure and neurological defects if ingested, Esposito said. In recent weeks, Suffolk County and Brookhaven Town officials have proposed separate plans to require or encourage installation of upgraded sewage treatment systems to protect lakes and streams.