Police and medical personnel searched Lake Mohegan in Fairfield after someone reported seeing a swimmer go under the water.
Fairfield police spokesman Lt. Jim Perez said authorities received the report of a 10-year-old boy who went into the water late Friday afternoon and did not resurface.
The lake is private and swimmers must scan in with an ID while on the grounds. Everyone who scanned in on Friday is accounted for, according to fire officials.
Divers searched the lake as a precaution. The search ended just before 7 p.m.