What happened
A commercial certificated pilot was operating a float-equipped airplane in cruise flight at approximately 800 feet above ground level when the engine began to lose power. In an attempt to rectify the issue, the pilot switched the fuel tank selector from the right tank to the "BOTH" position. The engine continued to operate for approximately two minutes before losing power again. The pilot did not apply carburetor heat during the event.
The pilot identified a suitable forced landing area on a small, marshy lake and executed the landing. Following the touchdown, the pilot observed damage to the leading edge of the left horizontal stabilizer, which appeared to have been caused by striking a tree limb during the emergency descent and landing. The pilot, who is also a certificated mechanic, subsequently replaced the entire leading edge of the stabilizer.
The investigation
An examination of the aircraft following the event revealed no obvious mechanical engine problems. The wing fuel tanks contained between 1.5 and 2 inches of fuel, and inspections of the fuel screens and fuel tank sumps showed they were clean. The pilot noted a suspicion that the power loss may have been caused by carburetor icing or water contamination in the fuel.