The pilot reported that he was returning to land after dropping a load of skydivers at 10,000 ft above mean sea level, and that he did not apply carburetor heat during the descent. He reduced the throttle to idle when he entered an extended based leg of the traffic pattern. The approach path was low, so the pilot increased the throttle, but the engine did not respond. He completed steps to troubleshoot the loss of power, but he did not apply the carburetor heat. The pilot made a forced landing to a marshy area; the airplane impacted uneven terrain and sustained substantial damage to the left wing. Examination of the fuel system did not reveal any anomalies that would have precluded normal operation. The atmospheric conditions at the time of the accident were conducive to the development of serious carburetor icing at glide power. Given the evidence, it is likely that carburetor ice accumulated, which resulted in the inability to increase engine power during the final approach. According to the Federal Aviation Administration, the airplane’s engine is highly susceptible to ice formation during a descent and the use of carburetor heat is recommended.