On July 16, 1999, approximately 0834 central daylight time, a Bell OH-58A helicopter, N9254R, was substantially damaged when it impacted terrain during a forced landing following a total loss of engine power near Bastrop, Louisiana. The instrument-rated commercial pilot, sole occupant of the helicopter, was not injured. The helicopter was registered to and operated by North Star Helicopters Inc., of Jasper, Texas. Visual meteorological conditions prevailed for the 14 Code of Federal Regulations Part 137 aerial application flight and no flight plan was filed. The local flight originated from a private staging area near Bastrop, Louisiana. According to the pilot, he had completed his 30th application of arsenal, a chemical used for aerial application flights, and was returning to the staging area. The helicopter was flying at 150 feet agl when the engine power "gradually decreased," and the engine lost total power. The pilot stated that the "ENGINE OUT" warning light illuminated. He initiated an autorotation, during which the helicopter contacted pine trees that were approximately 20 feet tall. The helicopter came to rest on its left side in the pine trees. The tail boom, the left skid, and the main rotor blades were damaged. The FAA inspector, who visited the accident site, reported that the helicopter's fuel system was contaminated with water and algae. He stated that water and algae were found in the helicopter's fuel filters. According to the operator, the refueling truck had been contaminated with water a few days prior to the accident. The accident helicopter was fueled from the contaminated truck. The ground crew and pilot became aware of the situation and sumped the helicopter's fuel tanks and the refueling truck. The pilot thought he had sumped all of the water out of the helicopter's fuel tanks. The pilot took the helicopter on the first flight since the discovery of contamination and experienced the ensuing engine failure. The operator stated that the filter on the refueling truck had failed to separate the water from the fuel during the fueling operations. The operator reported that all of its refueling trucks have since been modified with additional water/fuel separators as an extra measure of safety.