The airplane received substantial damage during a forced landing on a lake. The pilot reported a total loss of engine power while maneuvering over a lake at 300-500 feet above ground level. Post-accident examination revealed no fuel in the left fuel tank and a mixture of water and fuel in the right fuel tank. The fuel selector was selected to the left tank. There was no fuel found in the gascolator. The airplane rudder was "folded" over. The pilot reported minor injuries.