On October 1, 1993, at 1015 Pacific daylight time, a Cessna 182H, N8397S, operated by the pilot, collided into the Clear Lake (fresh water) Reservoir and sank. The accident site was in northern California about 35 nautical miles east-southeast of the Klamath Falls International Airport, Oregon. The airplane was substantially damaged and the private pilot was not injured. The passenger, a retired airline captain, was fatally injured. The flight originated from Klamath Falls at 0950. The pilot reported that visual meteorological conditions prevailed during the personal flight, and he did not file a flight plan. After taking off, he proceeded to fly in the direction of the Clear Lake Reservoir. In the pilot's completed "Aircraft Accident Report," NTSB Form 6120.1, he wrote that while en route, "...we both took turns doing wing overs and tight turns." Upon arriving over the lake, the pilot commenced a left turn. The pilot explained the mishap in the following manner: "Half way across the island, we decided to make a 360-degree turn to the left over water, and then go home. We were half through the turn when there was an optical illusion with no horizon and flew into the water...." The National Transportation Safety Board interviewed the pilot on October 2, 1993. The pilot reported that when the accident occurred he had been flying the airplane. The pilot stated that during the last turn he had lost his reference, and then the airplane contacted the water and sank. No mechanical problems were experienced during the flight.