State parks officials closed Southwick Beach Friday after tests showed the presence of E. coli in the waters of Lake Ontario.
E. coli is a bacteria.
Some strains can cause vomiting and diarrhea in people who swallow the bacteria.
Officials closed the beach after two separate tests confirmed the presence of E. coli in Lake Ontario near the beach.
No illnesses were reported.
"This is a very unusual incident here at Southwick Beach in recent memory. We cannot recall having to close the beach," said Kevin Kieff, director of the Thousand Islands Region of the state Office of Parks, Recreation and Historic Preservation.
Officials are now waiting for the water to clear up naturally.
They hope to reopen the beach by Saturday afternoon if tests for E. coli come back negative.