The pilot of the homebuilt Searey amphibious airplane had completed one uneventful landing on a river. The pilot stated that during his second landing, because of the glassy water conditions, he stayed close to the shoreline to better judge the water elevation, and utilized glassy water landing techniques. He further stated that he did not manipulate the landing gear handle after the first landing, and verified that the gear was up prior to the second landing. During touchdown, the airplane nosed over, and partially sank. The windshield fractured, and the airframe was substantially damaged. The landing gear was observed partially extended by recovery personnel; however, examination of the airplane, which included the landing gear system, did not reveal any pre-impact failures. The pilot reported 689 hours of total flight experience, which included 65 hours in the same make and model as the accident airplane.