The pilot reported that he was landing the float equipped airplane on a lake. The winds were light and the lake had about 3 inch ripples on the water. He reported that the touchdown appeared normal, but a few seconds later the right wing went up and the left wing dipped in the water. The left wing was bent upward and sustained substantial damage. A witness reported that he observed the airplane flying slow over the water in a left bank when the airplane “dropped into the lake” with the left wing hitting the water. The pilot reported there was no mechanical malfunction of the airplane.