On July 18, 2001, about 1430 Alaska daylight time, a wheel-equipped de Havilland DHC-2 airplane, N9262Z, sustained substantial damage during a forced landing, about 3 miles west of Willow, Alaska. The airplane was being operated as a visual flight rules (VFR) cross-country government flight under Title 14, CFR Part 91, when the accident occurred. The airplane was owned by the USDA Forest Service, and operated by the State of Alaska, Department of Natural Resources, Forestry Division. The certificated airline transport pilot and the two passengers aboard were not injured. Visual meteorological conditions prevailed, and VFR flight following procedures were in effect. The flight originated at the Lake Hood Airstrip, Anchorage, Alaska, about 1230. During a telephone conversation with the National Transportation Safety Board investigator-in-charge on July 19, the pilot reported he was conducting an aerial timber survey. While in cruise flight about 1,000 feet above the ground, the pilot said the engine began to backfire, run rough, and lose power. He said he activated the engine wobble pump fuel pump, and switched fuel tanks, even though each fuel tank contained adequate fuel. The engine then quit, and the pilot said he selected a gravel bar along a glacial fed river as an emergency landing area. He said that during the emergency approach to landing, the airplane landed short of the intended landing site, touched down in about 3 feet of water, and nosed over. The airplane sustained substantial damage to the wings and vertical stabilizer. After the airplane was recovered, a Federal Aviation Administration (FAA) airworthiness inspector from the Anchorage Flight Standards District Office (FSDO), examined the airplane in Palmer, Alaska, on July 19. The inspector reported that the number seven cylinder was cracked, the number nine cylinder had no compression, and that about one cup of clear water was found within the carburetor float bowl. The inspector reported that he was unable to determine if the cylinder damage, or the presence of water in the carburetor was a result of postimpact damage with the river water. The engine was sent to Tulsa Aircraft Engines, Inc., Tulsa, Oklahoma, for inspection and repairs. In a letter dated October 29, 2001, a representative from Tulsa Aircraft Engines, Inc., reported that when the engine was disassembled, the number nine cylinder head was found separated from the cylinder barrel.