The pilot of the amphibious airplane reported that he made a normal approach to landing with near glassy water conditions. Shortly after contact with the water, the right sponson separated and the right wing impacted the water, causing the airplane to spin 180 degrees and come to a stop. The pilot attempted to water taxi to shore, but the cabin area began taking on water. Before reaching the shore, the pilot and passenger decided to perform an emergency evacuation and boarded a boat that had come to provide assistance. The airplane sunk after the pilot and passenger evacuated the airplane. During a post-accident interview with the pilot, he stated that "the right wing may have dipped" during landing and reported "significant damage" to the right wing flap after the sponson separated during the touchdown. The airplane was later recovered, but the right sponson was not located. A Federal Aviation Administration Aviation Safety Inspector observed damage to the right wing at the wing root and noted the sponson detachment does not appear to have been due to any design or assembly issue. The pilot reported no mechanical malfunctions or failures with the airplane that would have precluded normal operation. The airplane sustained substantial damage to the right wing and fuselage.