Incident Overview
A private pilot was continuing a cross-country flight after a fuel stop. Approximately 20 minutes after departure, the pilot reported that both engines began running rough. He turned the airplane toward the nearest airport and initiated a descent. Concluding that the airplane would not reach the airport and citing rugged terrain below, the pilot elected to ditch the airplane in a large lake over which he was flying.
Pilot's Account
The pilot stated that no mechanical anomalies existed prior to the loss of engine power. He expressed a belief that fuel contamination caused the engine problem and suggested that avoiding refueling during heavy rain might have prevented the issue.
Investigation Findings
Fuel samples were taken from the supply where the pilot added fuel and from the equipment used to fuel the airplane. No other reports of fuel contamination were received. According to an FAA inspector, the samples were tested and found to be clean. The airplane was not recovered from the lake and has not been examined by the NTSB.
Probable Cause
The official probable cause is the loss of engine power during cruise flight for an undetermined reason.