What happened
The aircraft struck a gravel bar while taxiing on the water. Due to a receding tide from the previous night, the plane remained stuck until the following morning. Approximately three hours later, as the pilot continued to taxi in anticipation of daylight for takeoff, the aircraft rolled over into the water and eventually sank.
Prior to the incident, the pilot observed two one-inch dents on the submerged float with bubbles escaping from them. The pilot noted that these floats routinely leaked and required daily pumping, but this maintenance was not performed between the time the aircraft grounded on the gravel bar and when it sank. There were no approved personal flotation devices aboard.
The four individuals on board attempted to swim for shore using inflated hip waders. Two of these individuals were lost and are presumed drowned in the attempt. The water temperature was approximately 45 degrees Fahrenheit.