The pilot of the amphibious airplane departed from a land-based airport with hard surfaced runway. After conducting some local sightseeing, he prepared to land on a nearby lake. As the airplane settled onto the water it nosed over. The pilot and passenger egressed the airplane and sustained minor injuries, and the fuselage of the airplane was substantially damaged. Following the accident, the pilot noticed that the airplane’s landing gear was in the extended position. He then realized that he had failed to retract the landing gear after departure from the hard surface runway, and inadvertently had left them extended for the water landing. He further described that he allowed his conversation during the sightseeing portion of the flight to distract him from correctly configuring the landing gear. The pilot reported that there were no preaccident mechanical failures or malfunctions of the airplane that would have precluded normal operation.