Wardens released the above photo of authorities responding Saturday morning to Pocasset Lake near the southeast shore.
Officials with the Maine Warden Service said Christopher Brown, 33, of Wayne, was last seen late Friday evening leaving a gathering of friends, and wardens believe he died at some point during the night.
He was found shortly before 10 a.m. when a passerby saw what they thought was an abandoned boat.
Officials said the boat appeared to have hit rocks just under the surface of the water.
The area is marked with a hazard.
Brown was not wearing a life jacket but they were found in his motorboat.
His body has been taken to the medical examiner for further investigation.