During takeoff from Long Haul Lake, the engine failed. An engineer was flown in to troubleshoot the problem. Water was drained from the main fuel-filter and carburettor sumps. Two run-ups were conducted following which the pilot and engineer tried to take off. Shortly after takeoff, the aircraft’s engine abruptly lost power. The pilot’s attempts to restart the engine were unsuccessful, and the aircraft descended into a stand of trees and struck the ground. FINDINGS AS TO CAUSES AND CONTRIBUTING FACTORS: – The most likely accident scenario during the second take-off is that water contamination migrated from the centre fuel tank to the engine, resulting in a loss of engine power. – The engine stopped at a point from which there was insufficient time for the engine to restart, nor from which a safe landing could be made. – Indications of water contamination were found in the fuel system after the occurrence; however, the source(s) of the water contamination could not be identified.