THE ACFT WAS ON A SCHEDULED FLT FROM ANCHORAGE TO COLD BAY, AK WITH INTERMEDIATE STOPS AT KING SALMON & DUTCH HARBOR, AK. EN ROUTE BETWEEN ANCHORAGE & KING SALMON, THE AIR TEMPS AT CRUISE ALTITUDE WERE BETWEEN -36 & -40 DEG FAHRENHEIT. WHILE ENTERING DONWND TO LND AT KING SALMON, THE BEFORE-LNDG CHECK WAS MADE WHICH INCLUDED TURNING OFF THE FUEL HEATERS.SHORTLY THEREAFTER, THE R ENGINE LOST PWR & WOULD NOT RESTART. THE R ENGINE WAS FEATHERED & SECURED. SOON AFTER THAT, WHILE TURNING TO FINAL APCH WITH THE GEAR DOWN, THE L ENGINE BEGAN LOSING PWR. THE CAPTAIN ELECTED TO LAND ON A FRZN RIVER & CALLED FOR THE GEAR TO BE RETRACTED. WHILE LNDG, THE ACFT TOUCHED DOWN BEFORE THE GEAR WAS FULLY RETRACTED. AN INVESTIGATION REVEALED ALL 3 TURBINE STAGES OF THE L ENGINE WERE DAMAGED FROM OVERHEATING, INDICATIVE TO EXCESS FUEL FLOW. EXCEPT FOR THE L ENGINE OVERHEATING, NO OTHER MECHANICAL DEFECTS WERE FOUND WITH EITHER ENGINE. HOWEVER, ENTRAINEDWATER (WTR IN SOLUTION) CAN OCCUR IN JET FUEL. WATER (29 TO 150 PPM) WAS FOUND IN FUEL SAMPLES. CONDS FOR ICE, PRESENT.