The pilot was on an instrument flight rules flight. The controller cleared the pilot for a VOR runway 22 approach at the destination airport. The pilot initiated a descent and did not apply carburetor heat. The Let-Down procedures in the checklist states, "Carburetor Heat-AS REQUIRED to prevent carburetor icing." Upon reaching the minimum descent altitude for the approach, the pilot increased the throttle and did not get an engine response. The pilot realized he could not make the runway and made a forced landing into a river. The surface weather observation at the destination airport revealed the temperature was 75-degrees Fahrenheit and the dew point temperature was 61-degrees Fahrenheit. Review of the Department of Transportation Icing Probability Chart indicates the airplane will encounter serious icing conditions at glide power. The engine was mounted in a test stand and an alternate fuel, and battery source was attached. Engine controls, and magneto grounding wires were installed. The mixture control was safetied wired in the full rich position. The engine was started and ran at idle power. After engine warm up the throttle was advanced to full power and the engine stabilized at takeoff rpm of 2,000. The throttle was returned back to the idle position, the safety wire on the mixture was cut, and the engine was shut down with the mixture control.