What happened
The pilot was attempting to perform a takeoff from a remote lake when the hydraulically actuated flaps on the aircraft retracted from the fully extended takeoff position to a 1/2 position at the start of the water run. The pilot reported that the airplane reached the 'on step' phase normally and he subsequently attempted to pump the flaps back to the fully extended position.
However, the aircraft failed to become airborne. During this process, the pilot realized that the flap selector handle was in the 'up' position rather than the required 'down' position. As a result of the failure to lift off, the airplane struck a four-foot-high bank at the end of the lake. The impact caused the floats to separate from the aircraft. The pilot was not injured.
Findings
The investigation focused on the positioning of the flap selector handle. While the pilot initially indicated that he had forgotten to switch the handle to the 'down' position, a later statement suggested that he believed he had positioned it correctly. He noted that his shirt sleeve may have snagged the handle and inadvertently repositioned it during the takeoff run.