On September 21, 1995, about 1244 eastern daylight time, an Air Tractor 502, N1529E, registered to and operated by Glades Ag Service, Inc., crashed into Lake Istokpoga near Lorida, Florida. Visual meteorological conditions prevailed at the time and no flight plan was filed for the 14 CFR Part 137 aerial application flight. The airplane was substantially damaged and the commercial-rated pilot was fatally injured. The flight originated about 1245 from a private airstrip near Lake Placid, Florida. According to an employee of the operator, while loading the hopper with the engine operating, he observed that the fuel tank gauge in the cockpit indicated 1/4. He advised the pilot to refuel which is normally accomplished at the Sebring Airport, Sebring, Florida. The pilot advised him that he would spray only part of his load then fly to Sebring. The flight departed to spray a sod farm which was located south of Lake Istokpoga. A witness who was in a boat about 1 mile south of the crash site on the north side of the lake, observed the airplane spraying chemical over the lake. He then observed the airplane descend into the water. The airplane was located inverted in about 5 feet of water. Divers who recovered the pilot's body stated that the cockpit doors were open, the pilot's seat restraint was unlatched, and he was not wearing a helmet. According to the sheriff's department investigator, the seat restraint system is a four place, military style type. During recovery of the airplane the fuel tanks were drained using the sump drains and about 2 gallons of fuel and water were recovered. The airplane was taken to a nearby airport for further examination. Examination of the airplane by an FAA airworthiness inspector revealed that the cockpit doors were in the open position with no evidence of failure or malfunction of the latch assemblies. Examination of the fuel system revealed that the header tank which by design holds 1.23 gallons of fuel contained only several drops of water. The airframe fuel filter which by design holds 38 1/2 fluid ounces of fuel was drained and found to contain about 2 tablespoons of fluid which appeared to be a combination of jet fuel and water. The engine fuel pump discharge filter cover was removed and found to be about 1/8 to 1/4 full of jet fuel. No solid or liquid contamination was noted of the fuel drained from the fuel pump. Examination of the flight controls revealed no evidence of preimpact failure or malfunction. Post-mortem examination of the pilot was performed by Alexander Melamud, M.D., District Ten Medical Examiner. The cause of death was listed as drowning. The autopsy report indicates five superficial abrasions were located on the lower middle and right aspect of the forehead. Toxicological analysis of specimens of the pilot was performed by the Wuesthoff Memorial Hospital. The results were negative for tested drugs and ethanol.