On June 12, 1996, at 1100 hours Pacific daylight time, a Cessna 150H on floats, N22474, was substantially damaged when the right float dug into the water and the aircraft nosed over during landing on Melones Reservoir at Angels Camp, California. The private pilot was not injured. Visual meteorological conditions prevailed for the local area personal flight. The operator told the NTSB investigator that the pilot rented the aircraft the previous day and practiced landings on Melones Reservoir prior to camping out overnight. The pilot told the operator that the following morning the right float was low in the water, and that it took about 330 pumps with the bilge pump to empty the float. The pilot then practiced more takeoffs and landings, stopped to refuel the aircraft, and returned to practice more takeoffs and landings when the accident occurred. He estimated performing 45 takeoffs and landings between the time he pumped out the float and when the accident occurred. The operator reported that there were two holes in the right float when the aircraft was recovered that had apparently been made the previous day. In his accident report, the pilot stated that he had received his single engine sea rating 10 days prior to the accident, and that this was the only float plane he had ever flown. It routinely took 80 pumps of the bilge pump as part of the preflight activities during his instruction and he "assumed that pumping the float a great deal was okay and did not pose a problem." When the float required over 330 pumps on the morning of the accident he thought this unusual, but considered the number of landings the previous day and the fact that the aircraft had been in the water overnight.