The swimming beach at Moreau Lake State Park has closed.
Park officials made the announcement on Tuesday, and said a potential harmful algal bloom in the water forced the decision.
"Samples have already been gathered and are at the lab for confirmation," read a statement on the park's website and Facebook page.
Beach status updates will be posted online.
According to the National Ocean Service, harmful algal blooms occur when colonies of algae - simple photosynthetic organisms that live in the sea and freshwater - grow out of control while producing toxic or harmful effects on people, fish, shellfish, marine mammals and birds.
Human illnesses caused by the blooms, the service says, can be fatal in rare cases.
Last Saturday, a power outage forced the beach to close during morning hours. And in June, officials posted warnings about "swimmer's itch," caused by common lake water organisms.
The beach is located off Old Saratoga Road.