According to the pilot, the flight was uneventful; however, as he flared the airplane in ground effect, it floated and overran the runway coming to rest inverted, in about 6 feet of water. He was unable to recall if he applied power to the engine in order to perform a go-around. An eyewitness reported that the airplane's landing gear did not make contact with the runway surface and subsequently contacted mangrove vegetation at the departure end of the runway prior to the airplane nosing over into the water. The airplane sustained substantial damage to the left wing. The pilot reported no pre-impact mechanical malfunctions or abnormalities with the airplane that would have precluded normal operation.