FACTUAL INFORMATION Following a normal climb, the pilot dropped two parachutists over Hamilton Island. A power-off descent to circuit height followed. The pilot did not select Carburettor Heat during the descent. When on a long final approach the pilot attempted to arrest a high descent rate with the use of engine power. The engine failed to respond. The pilot found that the aircraft was outside gliding range of the runway and he decided to ditch the aircraft in shallow water. Engine trouble checks failed to restore power to the engine. The aircraft was ditched in shallow water and after a successful escape from the cabin, the pilot was picked up by an island launch. The aircraft's engine was transported to a maintenance facility at Archerfield where it was examined. The engine was extensively corroded by salt water. No fault was found as far as could be determined. The Bureau of Meteorology data showed that the relative humidity at ground level was 65%. The Carburettor icing - probability chart showed that serious icing at descent power was to be expected at such a humidity level. ANALYSIS Although there are other possible reasons for the power loss, it is most likely that the engine failed to produce power due to carburettor icing.