The pilot of the amphibian airplane reported that he was attempting to land on a lake with a tailwind. He circled the landing zone once and verified that there was no debris in the water. During the landing flare, the airplane floated beyond the intended touchdown point and was nearing the shore. The pilot initially added power to go-around, but then reduced power when he did not think the airplane would clear the trees near the shoreline. The airplane subsequently nosed over and came to rest in the water. Examination of the airplane by a Federal Aviation Administration inspector revealed substantial damage to both wings and the fuselage. The landing gear was retracted into the floats. The pilot added that there were no preimpact mechanical malfunctions with the airplane.