According to the pilot, after landing the float-equipped airplane in a canal where aircraft were prohibited from landing, he was directed by law enforcement personnel to depart in a northwest direction. The pilot subsequently performed a normal takeoff, and after becoming airborne he banked the airplane to the right and continued to climb in a nose-high attitude. The nose then dropped and the airplane impacted the water. After noticing a puncture hole in the right float, the pilot ascertained that the airplane must have struck an obstacle in the water during the takeoff. A postaccident examination of the airplane by a Federal Aviation Administration (FAA) inspector did not reveal damage consistent with an obstacle impact. Detailed maps of the canal did not reveal any exposed rocks along the takeoff path and the nearest obstacle would have been 4 feet below the water line. The FAA inspector also viewed a video of the accident flight, which showed the airplane taking off in a level attitude, then commencing a shallow bank right-hand turn. Initially the airplane climbed, but as the angle of bank increased, the nose pointed down to below the horizon and then descended until impact. The pilot reported no preimpact mechanical anomalies with the airplane.