CHICAGO (CBS) — Chicago students filming a documentary found a body in the water Monday afternoon at Rainbow Beach.

The teens made the gruesome discovery around 5:50 p.m., near 75th and Lake Shore Drive. They spotted the body in the water, and immediately called 911.

Police said it’s not clear how long the body had been in the water, or how it got there.

“The water’s kind of murky, so we can’t really tell,” said Police News Affairs Officer Jose Jara. “Some students were doing some documentary along the bank here, and that’s where they discovered it.”

The body has not been identified, but police believe it was a man.