On July 1, 1994, approximately 1300 mountain daylight time, a Piper PA-38-112, N24201, sustained substantial damage during takeoff from Copenhaver airstrip, an unimproved airstrip about fifty miles northeast of McCall, Idaho. The private pilot and his passenger were uninjured. No flight plan was filed for the flight. Visual meteorological conditions prevailed. The ELT did not activate. The pilot stated that he did a preflight, runup, and full power takeoff using one notch of flaps. He said that the aircraft lifted off and remained in ground effect for a couple hundred feet before reaching the end of the 1100 foot runway and descending into the river. The pilot had flown into the airstrip about 0900. Boise, Idaho weather was clear, with temperature of 86 degrees, and barometric pressure of 29.96, at 1300. The pilot did not provide an accident report. The operator stated that, earlier that day, he had told the pilot--who wanted to go fishing--not to take the aircraft into several longer airstrips.