According to the pilot, he departed from a hard-surfaced runway for a flight to, and touch-and-go landing on, a lake approximately about 3 miles away. The touchdown on the lake was normal, but immediately after making contact with the water, the airplane abruptly decelerated and nosed over. The airplane sustained substantial damage to the nose and fuselage. Postaccident examination revealed that the landing gear was in the extended and locked position; however, the position of the landing gear switch at impact could not be confirmed because of possible movement during the shutdown and recovery. Initially, the pilot stated that he "forgot to put the wheels up." Later, he reported that he raised the gear after the departure. However, no preaccident mechanical malfunction or failures were found that would have precluded normal gear retraction for a water landing. Thus, based on the evidence that the airplane nosed over immediately after touchdown and that the landing gear was extended and locked after impact, it is likely that the landing gear was not retracted after takeoff.