On February 25, 1994, at 1750 eastern standard time, a Piper PA-28-140, N7313J, registered to William G. Burton, ditched in a lake following loss of engine power, shortly after takeoff from Kendall-Tamiami Executive Airport, Miami, Florida, while on a 14 CFR Part 91 personal flight. Visual meteorological conditions prevailed at the time of the accident and no flight plan was filed. The aircraft received substantial damage and the airline transport-rated pilot received minor injuries. One passenger received serious injuries and one passenger received minor injuries. The flight was originating at the time of the accident. The pilot stated that shortly after takeoff while climbing through 600 to 800 feet the engine quit abruptly. All attempts to restart the engine were unsuccessful. He then ditched the aircraft in a lake, 1/2 mile from the airport. Postcrash examination of the aircraft after it was recovered from the lake indicated all fuel and fuel vent lines were free of obstructions. The left fuel tank contained about 20 gallons of 100LL aviation fuel. The right tank was damaged and did not contain any fuel. The fuel selector was found on the left tank position. The carburetor was found to contain a mixture of water and fuel. All engine controls were attached. The engine air filter and air intake hose from the filter box to the carburetor was not recovered after the accident. The electric fuel boost pump switch was found in the on position. The electric fuel boost pump was found unobstructed and to operate normally. The engine was removed from the aircraft and mounted in a engine test cell. After drying the water from the magnetos the engine was started and operated to full power with no evidence of failure or malfunction. The carburetor accelerator pump nozzle was found missing from the carburetor inlet. This did not effect engine operation. Testing of water and fuel samples removed from the carburetor after the accident and water removed from the lake in which the aircraft crashed was performed by Microchemical Analysis Branch, NASA Kennedy Space Center, Florida. The water in the carburetor bowl had similar properties to water from the lake. See attached report.