Prior to departure the commercial pilot attempted to remove frozen contamination from the wings of the float equipped airplane, but some contamination remained. During the takeoff run, the airplane failed to become airborne before reaching the end of the lake. The airplane slid along a gravel spillway for several hundred feet, before nosing over. The airplane sustained substantial damage to the wings, empennage, and fuselage. The pilot stated there were no pre-accident anomalies with the airplane that would have precluded normal operation. In the pilot’s written statement to the National Transportation Safety Board he noted that the accident might have been avoided if he had removed all the frozen contamination from the wing, or waited for above freezing temperatures.