On August 7, 2001, at 1851 Pacific daylight time, a Cessna 150L, N6688G, made a forced landing on a city street following a loss of engine power on approach to the airport at Fullerton, California. The airplane was substantially damaged during the landing roll when it collided with trees. The private pilot/owner was operating the airplane under the provisions of 14 CFR Part 91, and sustained minor injuries. The personal cross-country flight departed from Meadows Field, Bakersfield, California, about 1520. Visual meteorological conditions prevailed, and no flight plan had been filed. The Federal Aviation Administration (FAA) accident coordinator interviewed the pilot. The pilot said that he added 8 gallons of fuel in Bakersfield. The engine began to run rough and lost power passing through 2,000 feet as the airplane approached Fullerton. The pilot started the engine, but it continued to run rough, and stopped producing power again. He didn't think he could glide to a school yard so he elected to land on the city street and the wing collided with a tree. The pilot drained about 8 gallons of fuel from the wings following the accident. The FAA accident coordinator inspected the airplane. He removed a plug on the bottom of the carburetor and drained about 1 ounce of fuel. He observed water and a white substance in the fuel strainer. The carburetor was examined at Precision Airmotive Corporation under the surveillance of an NTSB investigator. There was a white, sandy substance in the carburetor bowl, and a ball of fibrous contamination in the inlet screen that blocked approximately 15 percent of the screen. Repeated requests were made to the pilot to complete NTSB Form 6120.1/2, but no response was received.