On August 25, 1998, about 1548 eastern daylight time, a Cessna 185, N114LS, was substantially damaged as it flipped over while performing a water landing on the Westport River, Westport, Massachusetts. The certificated flight instructor and private pilot were not injured. Visual meteorological conditions existed and no flight plan was filed for the instructional flight conducted under 14 CFR Part 91. The flight originated from New Bedford Regional Airport (EWB), New Bedford, Massachusetts, about 1500. After departing EWB, the flight instructor and private pilot proceeded to the South Wattupa Pond, where they performed several water maneuvers demonstrating the handling characteristics of the float airplane. The flight instructor stated that during one of the maneuvers, while moving the controls, a loud noise was heard in the empennage. He stated that when he checked the flight controls, everything moved correctly, so they continued the flight towards the Westport River. Upon arriving at the Westport River, the flight instructor directed the pilot to perform a power off landing (simulated engine failure). When it became apparent to the flight instructor that the airplane was not going to reach the intended point of landing, he suggested to the pilot to complete a turn and land on another section of the water. The flight instructor stated that on final approach, the airplane's pitch attitude began to oscillate up and down, and after two quick cycles, he attempted to take control of the airplane. Unable to arrest the rate of descent, the airplane contacted the water and bounced. The instructor initiated a full power go around, but was unable to maintain control. The airplane impacted the water a second time, cartwheeled, and came to rest inverted in the water. The private pilot reported that they had initiated a simulated engine out landing on the Westport River. He stated that they "wanted to land south of the bridge," but decided against it due to a "lack of gliding distance." A turn to the north was initiated, and they set up an approach for landing, "a little quick and with a tailwind." The airplane impacted the water, and "full power was given"; however, the airplane "had lost lift, veered right, and went inverted." The private pilot reported hearing no unusual sounds in the empennage, and did not experience any flight control malfunctions or uncommanded oscillations. A witness reported that the airplane "appeared to make a normal landing until it hit the water rather hard." She observed the nose of the airplane rise, the wings waver from side to side, and "it appeared, the pilot tried to take off again." She stated that the right wing "never really came back to a level position," and the airplane "continued to roll over upside down." Examination of the wreckage by a Federal Aviation Administration Inspector revealed no pre-impact malfunctions of the flight controls. The winds reported at EWB, at 1453, were from 220 degrees at 13 knots, gusting to 17 knots.