The aircraft was being operated on a business flight for the purpose of surveying farm crops in the area. At about 1700 EDT, it crashed into a 20 acre farm lake while on a westerly heading. The weather was reported as clear, visibility 6 to 7 miles with haze, temperature 90 degrees, and the wind was calm. Reportedly, the lake had a glassy surface. There were 3 witnesses that were fishing from a boat near the center of the lake. They reported that the aircraft passed along the south side of the lake on an easterly heading, circled and descended near the southeast corner of the lake, then came out of the turn and headed toward their boat. Witnesses estimated that the aircraft flew 10 to 30 feet over the boat, then struck the water with no change in engine sound. Divers found no bodies in the cockpit, the seat belt and shoulder harness were found hanging loose with no damage and no evidence of being latched during impact. An examination of the engine and aircraft revealed no preimpact failures.