WINDERMERE, Fla. — Law enforcement officials are still looking for a man thought to have gone underwater in a lake in Windermere early Sunday evening.

Divers were back out at Lake Down on Monday morning after the 37-year-old man vanished in the water at about 5 p.m. the day before.

Rescue workers said they're certain the man is in the lake, because his friends told authorities that he was the only one who didn't swim back to their pontoon boat.

The lake is about 18 feet deep where the man disappeared. His identity hasn't been released.

Investigators said the people in the boat got out for a swim in the middle of the lake. Later, they said they heard him screaming for help, then silence.

"After a short amount of time, they got out of the water. This male waved like he was in distress and went under," Lt. Ken Taylor said. "The people in the boat... tried to throw live preservers at him, (but with) the way of the current, the boat drifted away, and they never saw him again."

Deputies said the man was an experienced swimmer.

Lake Down is off of Conroy Windermere Road, about a mile away from Olympia High School.

Reporter Matt Fernandez contributed to this story.