On July 7, 2003, about 1450 Alaska daylight time, a float-equipped Helio H-391B airplane, N17081, sustained substantial damage when it collided with several trees during takeoff and initial climb at Big Lake, Alaska. The airplane was being operated as a visual flight rules (VFR) local area personal flight under Title 14, CFR Part 91, when the accident occurred. The airplane was operated by the pilot. The private certificated pilot, and the sole passenger, were not injured. Visual meteorological conditions prevailed. No flight plan was filed, nor was one required. During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), on July 9, the pilot reported that he departed Finger Lake in Wasilla, Alaska, and planned to do a touch and go at Big Lake. He said that during the departure from Finger Lake, he noticed the engine oil pressure flicker, and decrease to about 65 psi, which is near the low end of the normal operating range. He proceeded to Big Lake and landed near Crocker Island where he has a cabin. The pilot said he then began a takeoff toward the south, with about 5,000 feet of available space. During the initial climb, the oil pressure decreased to about 60 psi, and the engine rpm decreased to 3400 rpm. The airplane climbed to about 150 feet, and the bottom of the floats struck several tree tops at the south end of the lake. The airplane then descended to the ground and received damage to the wings and fuselage. The pilot said the wind was from the southwest about 3 knots, and the temperature was about 74 degrees. The pilot did not hold a seaplane rating. Following recovery of the airplane, the NTSB IIC examined the airplane on July 10. The throttle, propeller, and mixture controls were full forward at the instrument panel, and each control operated its respective component. The carburetor heat control was in the off position. The air intake was unobstructed. The engine contained 10 quarts of oil. The oil screen was free of contaminants. The crankshaft rotated when the propeller was turned by hand. Gear train continuity was established, and thumb compression in each cylinder was noted when the crankshaft was rotated by hand. The magnetos produced spark at all terminals upon hand rotation. The sparks plugs were dry and had a gray appearance. The engine fuel strainer contained clean, blue-colored fuel, and the screen was free of contaminants.