On June 23, 2012, at 1830 central daylight time, a Cessna model A150K airplane, N8380M, was substantially damaged during a forced landing near Mamou, Louisiana. The commercial pilot was not injured. The airplane was registered to and operated by the pilot under the provisions of 14 Code of Federal Regulations Part 91. Day visual meteorological conditions prevailed for the personal flight, which was operated without a flight plan. The local area flight departed the pilot's private airstrip near Mamou, Louisiana, about 1730. The pilot reported that the engine experienced a partial loss of engine power after encountering a momentary period of turbulence during cruise flight. He noted that the engine continued to operate smoothly at idle speed, but the engine was minimally responsive to multiple throttle movements. Specifically, a full application of the throttle would result in about 2,100 rpm for about 2-3 seconds before the engine went back to an idle speed. He subsequently engaged carburetor heat, which had no observed effect on engine operation. He proceeded to make a forced landing in a rice field, during which the airplane nosed over. The vertical stabilizer and rudder were substantially damaged during the accident. The engine, a Continental model O-200-A, serial number 199309-9-A, had accumulated 258.5 hours since its last major overhaul. A postaccident examination was completed by inspectors with the Federal Aviation Administration. The examination confirmed internal engine and valve train continuity as the engine crankshaft was rotated. Compression and suction were noted on all cylinders in conjunction with crankshaft rotation. The magnetos were adequately secured to the accessory section and provided spark as the engine crankshaft was rotated. The upper spark plugs were removed and exhibited features consistent with normal engine operation. There were no obstructions of the flexible induction tubing from the air filter housing to the carburetor. Mechanical continuity was confirmed from the cockpit engine controls to their respective engine components. The movement of the carburetor heat control confirmed continuity to the heat-box assembly. Examination of the carburetor and gascolator bowls revealed evidence of water and particulate contamination. The wing fuel tanks also contained water contamination. Additionally, an examination of the pilot/owner's refueling container, located on his private airstrip, revealed water and particulate contamination. The filter assembly installed on the refueling container was also contaminated with particulate debris. The closest weather observing station was at Allen Parish Airport (KACP), located about 15 miles northwest of the accident site. At 1815, the KACP automated surface observing system reported the following weather conditions: calm wind; visibility 10 miles; clear skies; temperature 35 degrees Celsius; dew point 17 degrees Celsius; altimeter setting 29.83 inches of mercury.