On October 28, 2006, about 1107 central daylight time, a Cessna 180B floatplane, N9117T, owned and piloted by a private pilot, received substantial damage on impact with Forest Lake, Forest Lake, Minnesota. 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 minor injuries, one passenger received no injuries, and two passengers received serious injuries. The two passengers were not restrained in their passenger seats and were ejected through the right door which opened in flight when the right float separated from the airplane. The local flight originated about 1103. The pilot stated in a written report that during the departure climb, the airplane pitched nose down, the airplane shuddered and the floats hit the water. The passengers fell into the lake and were floating near the ariplane floats, which seperated from the airplane. The pilot stated that the airplane became very hard to control, and he flew to a private airstrip where he performed an emergency landing. He stated that the float separated from the airplane due to an unknown failure. The pilot stated during a telephone conversation that he performed a preflight inspection and there were no problems noted with the airplane or its flight controls. He said that the flight controls were "fine," and the flight was within weight and balance limits. He stated that the total flight time after takeoff to impact with the lake was 30 seconds and that the airplane was not flying as "it usually does" since it "ate up a lot of lake" during the takeoff. He stated that he had to "horse" the airplane off the water to get it airborne. He stated that the engine was functioning "perfect." Once the airplane was airborne, it wanted to pitch down, but he kept applying nose up trim. He stated that he was able to climb to 100 feet above ground level before the airplane impacted the water about 100 miles per hour. He stated that he "feels" that what caused him to lose pitch control was due to a forward fitting hanging down on the "flying wire." A passenger stated that the accident flight was the second time she had flown with the pilot in the accident airplane. Her first flight was along what she thought was the St. Croix River at an altitude that was a "couple of feet" above the water and estimated that altitude as 10 feet, 15 feet, or 20 feet. She said that the pilot "seems" like a safe pilot. She stated that prior to the accident flight, the pilot did his "precheck," which she described as "pulling a couple of knobs and switches". After boarding the airplane, the pilot closed the right side door. The right seat passenger asked the rear seat passengers if they had their seat belts on. She said that she did not know why she and the other rear seat passenger did not put their seat belts on. After takeoff, the airplane climbed to an altitude that she said, "wasn't real high, about 10 feet above the water." She stated that when the pilot was "slumped" over the throttle; the airplane then descended. She was then ejected from the airplane. A witness stated that the airplane flew in from the east (Willow Point) and then dropped down low and touched the water about 800 feet from the witness's location. The airplane then started to wobble and looked as if the float caught the water which made the airplane go side to side and caused the floats to separate from the airplane. He stated that the airplane was still able to takeoff, and as it did, he saw two of the people aboard the airplane in the water as the airplane climbed to an altitude of 20-30 feet above the water. Another witness stated that he was looking south across the lake and saw an airplane with floats flying low, 10-15 feet above the water, towards the northwest and northwest shore. He stated that the "airplane altitude and high airspeed" is what caught his attention. His initial thought was that if the airplane was going to land it would not have enough distance in front of it to slow and stop before hitting the shoreline. As he continued to watch the airplane, it descended to the water striking the surface, with the float level, approximately 1,000 feet from the shoreline at a "very high rate of speed." The airplane bounced off the surface and became airborne again. He watched the airplane as it began to descend to the surface and at this point he lost sight of the airplane behind the trees on his shoreline. He then saw the airplane again as it was pulling up over the tree line on the northwest shore. He was surprised that the airplane was able to pull up with enough altitude to clear the trees. He continued to watch the airplane as it climbed and made a left 360 degree turn back over the lake. The airplane completed the turn and departed the area westbound. On July 1, 2006, the Forest Lake Police Department received a complaint about two float planes piloted by the accident pilot and his brother over Forest Lake. The complainant stated that the two float planes took off and flew at an "extremely low altitude" over several boats. The two planes then circled and flew towards each other and turned at the last minute. The complainant stated that the pilots frequently take off at boats and then maintain a "low altitude" while flying over the lake. On November 1, 2006, the Washington County Sheriff’s Office received a message from a resident on Forest Lake. The resident stated that for years the pilot and his brother have demonstrated "reckless flying" over Forest Lake. He stated that the accident pilot would perform "strafing runs" on his own (accident pilot's) house. The resident stated that on July 3, 2006, the accident pilot and his brother were deliberately trying to come within inches of the resident's boat in the middle of 3rd Lake. They then pulled up flying side by side a few feet apart. Examination of the floats revealed features consistent with overload and flight control system continuity was confirmed. No anomalies were noted that would have precluded normal operation.