On May 30, 2003, about 1430 Alaska daylight time, an amphibious float-equipped deHavilland DHC-2 airplane, N60TF, sustained substantial damage when it overturned during a wheels down landing on Salmon Lake, about 9 miles east-southeast of Sitka, Alaska. The airplane was being operated as a visual flight rules (VFR) local area nonscheduled cargo flight under Title 14, CFR Part 135, when the accident occurred. The airplane was operated by Harris Aircraft Services Inc., Sitka. The airline transport certificated pilot, the sole occupant, was not injured. Visual meteorological conditions prevailed, and a VFR flight plan was filed. The flight originated at the Sitka Rocky Gutierrez Airport, about 1419. During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), on May 30, the director of operations for the operator reported the pilot was landing on Salmon Lake to deliver supplies to a client at the lake. The airplane departed from a paved runway at Stika. The landing gear wheels were not retracted, and upon landing on the lake, the airplane nosed over and received damage to the left wing and fuselage. The airplane remained floating inverted. The director of operations said that the airplane is equipped with Wipline floats that have landing gear position lights installed on the instrument panel. The airplane also has a mirror enabling the pilot to visually observe the landing gear position. During a telephone conversation with the NTSB IIC, on June 2, the pilot reported that he was transporting several loads of equipment to the lake. He said he was distracted during the short flight when he had to reset the flaps, and by a minor malfunction with the airplane's GPS receiver. The pilot said he forgot to raise the landing gear after departing the Sitka Airport, and landed on the lake with the gear extended. In the Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1) submitted by the pilot, the pilot indicated that during the approach to the lake, he performed a "GUMP" (gas, undercarriage, mixture, prop) check while looking for a new unloading area. He said he failed to visually check the gear position.