What happened
The pilot reported that prior to departure, he fueled only the left tank of the aircraft, leaving the right tank empty. Approximately five to ten minutes into the flight, he initiated a five-degree left forward slip lasting about thirty seconds. Immediately upon returning the aircraft to level flight, the engine lost power. Despite attempting various procedures to restore engine operation, the pilot was unable to regain power.
He proceeded to make a forced landing on a small pond. As the aircraft slowed and transitioned off its step, the left float struck submerged willow sticks, causing the aircraft to sink. The left wing dropped and struck the water surface during this process.
The investigation
The pilot noted that the fuel tank in question lacks a drain. He explained that unless approximately one gallon of fuel is drawn through the gascolator, water contamination will not be visible.