Crews say no swimming is allowed at West Haven beaches after what they believe is black algae mixed with sewage was found on Wednesday.
Beachgoers spotted a large dark substance on Wednesday afternoon in the water.
The stretch of the black mass went from Savin Rock to Oak Street.
The U.S. Coast Guard and the Department of Energy and Environmental Protection responded to test the water. They believe it is black algae mixed with sewage.
People are allowed to go to the beaches, but have been told to not go into the water from Savin Rock to the water treatment plant, which is about a 2-mile stretch.
The water is being tested Wednesday night and Thursday.
On Wednesday, police tried their best to warn swimmers and fishermen about the issue, but it was a tall order.
The Gonzalez family was playing in the water when they smelled something awful.
"The smell it was like real nasty. The smell, it was unbelievable, it was nasty," said Hector Gonzalez.
Firefighters then showed up telling people to stay out of the water.
It is unclear if the nearby water treatment plant is part of the problem.
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