On September 11, 2004, about 2015 Alaska daylight time, a float-equipped Cessna 180A airplane, N5304D, sustained substantial damage during an emergency landing when it collided with terrain and nosed over following a partial loss of engine power. The accident site is near Windy Lake, about 22 miles east of Kasiloff, Alaska. The private pilot/airplane owner, and the sole passenger, were not injured. The local, 14 CFR Part 91 personal flight originated about 1800 from the pilot's residence, and operated in visual meteorological conditions without a flight plan. In the pilot's written statement to the NTSB dated September 16, he reported that the purpose of the flight was to look for potential moose hunting sites. He related that he initiated a low pass over a lake to see if it was suitable for landing. During the low pass, he noted that the carburetor heat was about 60% "on." After deciding the lake had potential as a landing site, he applied power to gain altitude, but the engine did not respond, and then it ran rough. He suspected carburetor ice, and pulled the carburetor heat control full on. At that point, the engine "choked," and started to die. The pilot indicated that they were then about 2 miles from the lake, about 200 feet above the ground. He did not believe he could return to the lake for a forced landing, and elected to land in a nearby swamp. While landing, the airplane's floats dug into the soft terrain, and the airplane nosed over, receiving structural damage to the vertical stabilizer and wing spars. The pilot said there were no preimpact mechanical problems with the airplane, and that the loss of engine power was due to carburetor ice. He noted that once the airplane was recovered from the swamp, the engine started and ran fine.