The commercial certificated pilot was landing a float-equipped airplane on the surface of a remote lake. The water surface was smooth and glassy. The pilot said he touched down too fast, and the airplane nosed over. The pilot, who was wearing an inflatable jacket, exited the inverted airplane and got onto the floats. The airplane sank in about two minutes. The pilot then swam for about 40 minutes to the shore. The pilot said the airplane is resting in about 250 feet of water, and has not been recovered.