At approximately 09:00 the pilot arrived at the private airstrip and prepared the ski-equipped de Havilland DHC-3 aircraft for the morning flight. This Otter was equipped with a turbine engine. Two passengers, with enough supplies for an extended period of time, including a snowmobile and camping gear, were to be flown to a remote location. The pilot loaded the aircraft and waited for the weather to improve. At approximately 12:00, the pilot and passengers boarded the aircraft and took off from the 3400 ft airstrip in an easterly direction. The aircraft got airborne near the departure end of the airstrip, and, shortly after takeoff, the right wing struck a number of small bushes and the top of a birch tree. The aircraft descended and struck the frozen lake surface, approximately 70 feet below the airfield elevation in a steep, nose-down, right-wing-low attitude. When it came to rest, the aircraft was inverted and partially submerged, with only the aft section of the fuselage remaining above the ice. FINDINGS AS TO CAUSES AND CONTRIBUTING FACTORS: “1. The pilot attempted to take off from an airstrip that was covered with approximately 18 inches of snow, and the aircraft did not accelerate to take-off speed because of the drag; the aircraft was forced into the air and was unable to climb out of ground effect and clear the obstacles. 2. The pilot did not abort the take-off when it became apparent that the aircraft was not accelerating normally and before the aircraft became airborne.”