On August 21, 2013, about 1356 Alaska daylight time, a Cessna 180, N7807K, sustained substantial damage when it impacted trees after takeoff from Walby Lake Seaplane Base (AA85), Palmer, Alaska. The airplane was registered to a private individual and operated by the pilot under the provisions of Title 14 Code of Federal Regulations Part 91. The commercial pilot, sole occupant of the airplane, sustained minor injuries. Visual meteorological conditions prevailed and no flight plan was filed for the local personal flight which was originating at the time of the accident. The intended destination was Finger Lake Seaplane Base (99Z), near Palmer. During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), the pilot reported that during takeoff to the west, the airplane felt sluggish after it became airborne. The pilot stated that as the airplane climbed to about 100 feet above ground level, he decreased the flap setting by one notch, and the airplane started to descend rapidly. Subsequently, the airplane impacted trees about 600 feet west of the lake. The pilot added that he felt he may have retracted the flaps from the third notch to the first notch, and stalled the airplane. He did not recall hearing the stall warning horn. Examination of the airplane by a Federal Aviation Administration (FAA) inspector revealed that both the left and right wings and fuselage were structurally damaged. The airplane was recovered to a secure location for further examination. Examination of the airplane by an NTSB investigator revealed that flap handle was in the second notch, or 20-degree setting. The stall warning horn was disassembled and produced a sound when suction air pressure was applied to the bell. The reed was intact, however, it was unable to be determined if the stall warning system was intact and calibrated due to the amount of impact damage to the wing and airframe. Review of recorded weather data from the Palmer (PAAQ) weather recording station located about 4 miles east of the accident site revealed that at 1353; wind was from 080 degrees at 8 knots.