On July 17, 1999, at 1930 central daylight time, a Cessna 180, N4636B, piloted by a private pilot, was substantially damaged shortly after it landed when it was struck by a power boat. Visual meteorological conditions prevailed at the time of the accident. The 14 CFR Part 91 personal flight was not operating on a flight plan. The pilot reported no injuries. The flight departed Tower, Minnesota, exact time unknown. According to the pilot, he had just landed the airplane on Vermillion Lake. He said he did not see the power boat approaching from his right side until a few moments before it struck his airplane's right float. A witness said the boat was travelling about 35 to 40 miles per hour as it rounded a bend in the lake and headed toward the boat. The witness said the boat did not turn until a few moments before the collision. The pilot said he tried to turn the airplane out of the boat's path. He said the airplane began a slow turn to its left just as the boat collided with its float. The pilot estimated the boat's speed was about 40 to 50 miles per hour.