The amphibious airplane was en route to its destination; at time of arrival the temperature was 75 degrees F and the dew point was 43 degrees F. These conditions were conducive to serious carburetor icing at glide power. The pilot stated upon entering the base leg he reduced power and began the descent for landing. While descending he reapplied power to which the engine was unresponsive. Actions by the pilot to restore power were unsuccessful and he initiated an off airport forced landing to a grass field northeast of the airport. Due to insufficient altitude the airplane struck a vehicle before the airplane stalled and impacted the ground. The airplane sustained substantial damage to the right wing and left wing lift strut. The pilot stated he was unsure whether there were any mechanical malfunctions with the engine but did believe the loss of power resulted from carburetor icing. A postaccident engine examination revealed no evidence of preimpact mechanical malfunctions or failures with the engine which would have precluded normal operation.