Incident Sequence
The pilot reported that while in cruise flight, the engine started to run rough. After all efforts to smooth the engine's operation failed, the pilot elected to make a precautionary landing on Fife Lake. The aircraft initially touched down on the lake surface normally. Shortly after landing, a loud noise was heard and water began to enter the cockpit. The aircraft subsequently sank in water estimated to be 25 to 30 feet deep.
Pilot Information
The pilot did not hold a seaplane rating at the time of the incident.
Witness Account
One witness stated that the aircraft lost power and dropped abruptly, slamming into the lake. This account differs from the pilot's description of a normal landing followed by water ingress.
Investigation Findings
The investigation did not reveal the reason for the loss of power. The cause of the engine roughness and subsequent power loss remains undetermined.