On June 11, 2007, at 0845 eastern daylight time, a Beech K35, N615T, was substantially damaged during a forced landing to a lake near Cross Junction, Virginia. The certificated private pilot was not injured. Visual meteorological conditions prevailed for the local flight, which originated at Winchester Regional Airport (OKV), Winchester, Virginia, at 0810. No flight plan was filed for the personal flight conducted under 14 Code of Federal Regulations Part 91. According to the pilot, he flew around the local area at an altitude of 1,500 feet for about 15 minutes. He then proceeded to a local lake, and maneuvered above it at 90-100 mph. As he initiated a right turn over the lake, the engine "sputtered." He leveled the airplane and applied full power, and the engine "came back" and sounded normal. The pilot switched fuel tanks, and since everything "seemed ok," he completed the right turn and leveled the airplane. Shortly thereafter, the engine then sputtered again and lost power. The pilot switched fuel tanks and attempted to restart the engine twice, unsuccessfully. He then performed a forced landing to the lake, and was able to egress the airplane prior to it sinking. The pilot reported he departed OKV with the main fuel tanks three-quarters full, and the wing tip tanks half full. He stated that after takeoff, he switched on the fuel transfer pump, to transfer fuel from the wing tip tanks to the main tanks. The airplane was last refueled 4 months prior to the accident flight. He had flown it twice since the last refueling. The most recent flight prior to the accident flight was 2 months prior. The airplane and engine were recovered from the lake and retained for further investigation. According to the salvage operator who recovered the airplane, approximately 50 gallons of fuel were drained from the main tanks, and the wing tip tanks were empty. The engine crankshaft was rotated by hand at the propeller flange and compression was obtained on all cylinders. Valve train continuity was confirmed on all cylinders to the rear accessory section. Water retained from submersion in the lake, was drained from the engine, and an engine start was attempted, but was unsuccessful. Examination of the airplane and engine logbooks revealed the most recent annual inspection was completed on August 8, 2006. No anomalies were noted, and the inspection was the last entry in the logbook. Weather recorded at OKV, approximately 13 miles to the southeast, at 0840, included calm wind, 10 miles visibility, clear skies, temperature 21 degrees Celsius (C), dew point 15 degrees C, and altimeter setting of 30.10 inches of mercury.