On September 20, 2002, about 0815 Alaska daylight time, a float-equipped de Havilland DHC-2 airplane, N144Q, sustained substantial damage during an in-flight collision with tundra-covered terrain during takeoff from a remote lake, located about 1 mile north of Bethel, Alaska. The airplane was being operated as a visual flight rules (VFR) local area instructional flight under Title 14, CFR Part 91, when the accident occurred. The airplane was being operated by Ptarmigan Air, Anchorage, Alaska. The first pilot, an airline transport certificated pilot/certificated flight instructor, seated in the right seat, and the second pilot, a commercial certificated pilot, seated in the left seat, were not injured. Visual meteorological conditions prevailed, and VFR company flight following procedures were in effect. The flight originated at the accident lake, about 0810. During a telephone conversation with a National Transportation Safety Board investigator on September 20, the first pilot reported that he was providing flight instruction/familiarization training to the second pilot. The first pilot said that just after takeoff, as the airplane climbed to about 50 feet above the water, the airplane began to buffet, and the right wing dropped. The airplane descended and subsequently struck an area of tundra-covered marshy terrain. The airplane sustained substantial damage to the wings, fuselage, and empennage. The first pilot reported that the accident flight was the first flight of the day. He added that a postaccident inspection of the airplane revealed an accumulation of frost on the wings.