On September 5, 2001, about 1430 Alaska daylight time, a float-equipped Cessna 180 airplane, N74806, sustained substantial damage during a forced landing at Big Lake, Alaska. The airplane was being operated as a visual flight rules (VFR) cross-country personal flight when the accident occurred. The airplane was operated by the pilot. The commercial certificated pilot, and the sole passenger, were not injured. Visual meteorological conditions prevailed. The flight originated from Lake Clark, Alaska, about 1300. During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), on September 28, 2001, the pilot reported that he was in cruise flight about 800 feet agl, when the engine began to lose power. He said he switched the fuel tank selector from the right tank to the "BOTH" position, and the engine continued to run for about another two minutes. He said he did not apply any carburetor heat, and the engine again lost power. The pilot selected a forced landing area on a small, marshy lake, known as "Donna's Pond." After landing, he noticed leading edge damage on the left horizontal stabilizer. He said the damage appeared to be the result of striking a tree limb during the emergency landing. The pilot, who is also a certificated mechanic, said he replaced the entire leading edge of the stabilizer. The pilot said that after the emergency landing, he did not find any obvious engine problem. The wing fuel tanks contained about 1.5 to 2 inches of fuel, and the fuel screens and the fuel tank sumps were clean. He said he suspected carburetor icing, or water in the fuel, as the engine problem. The pilot reported the weather conditions included calm wind, scattered sky conditions about 3,000 feet, a visibility of 8 to 10 miles, and the temperature was about 60 degrees F. Rain showers were in the area around Lake Clark, but in the area of the emergency landing, no rain was falling.