The pilot stated he was turning base to final in preparation for a water landing with his float equipped airplane. He reported the airspeed was 60 miles per hour. During the turn, at approximately 30 to 40 feet above the trees, the airplane began to sink and the left wing and nose dropped. The pilot further stated he had no time to recover as the aircraft impacted trees, and then the ground. He also stated that there were no deficiencies with the performance and handling of the airplane. The pilot explained that this accident may have been prevented if he performed a steeper approach with increased airspeed. The pilot reported that he had 2,070 hours of total flight experience, of which 172 hours were in the accident airplane make and model configured with floats. The recorded wind at an airport 15 nautical miles south southeast, about the time of the accident, was variable at 4 knots; however, the pilot reported rain showers in the vicinity accompanied by “rolling turbulence from the near by hills." Review of recorded weather at approximately the time and within a 30-nautical mile radius of the accident site did not reveal precipitation or wind gusts. Examination of the airplane revealed structural damage to both wings, wing struts, elevator and to the engine firewall.