An assistant fire chief said the teen was swimming with four friends when he disappeared while trying to reach a diving platform in the lake.
The victim was identified as Manuel Matias.
He was found in the water about 45 minutes later and taken to St. Vincent's Hospital in Bridgeport, where he was pronounced dead.
Police say Matias body was found 50 to 60 feet off shore in about seven feet of water. When his body was recovered, CPR was administered, but it was already too late. Members of his family were called to the scene when he went missing and were there when his body was recovered.
Sgt. Perez of the Fairfield Police Dept. says there have been three drownings there in the past 15 years.
