What happened
A commercial pilot was operating a float-equipped airplane on a flight departing from a lake. The pilot's intended route involved flying over a cabin located at the opposite end of the lake to notify the occupants of his departure. While cruising across the lake, the aircraft encountered a downdraft, which resulted in an impact with the water.
The impact caused the airplane to roll over and subsequently sink to the bottom of the lake. The pilot reported being knocked unconscious during the event and had no memory of specific details regarding the accident. A passenger on board was able to extricate the pilot from the aircraft and transport him to the shore. The aircraft sustained airframe structural damage during the impact.