On July 13, 2014, about 1300 central daylight time, a Piper PA 28-181 airplane, N9681K, impacted trees and terrain during a forced landing following a loss of engine power while on approach to land at the Waukesha County Airport, Waukesha, Wisconsin. The pilot and passenger received minor injuries. The airplane was substantially damaged. The airplane was registered to and operated by Wisconsin Fox River Flyers, Inc., under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. Visual meteorological conditions prevailed for the flight, which was not on a flight plan. The flight originated from the Watertown Municipal Airport, Watertown, Wisconsin, about 1220.The pilot reported that he had entered the airport traffic pattern for landing. When the airplane was abeam the approach end of the runway, he reduced power, applied carburetor heat, and confirmed that the auxiliary fuel pump was on. When the airplane was on the base leg of the traffic pattern, the pilot attempted to increase engine power but the engine did not respond. He stated that even full throttle did not result in an increase in power. He attempted moving the engine and carburetor heat controls to no avail. While attempting the remedial actions he had turned toward the runway and declared an emergency. The airplane impacted trees and terrain short of the runway resulting in substantial damage to the wings and fuselage. A postaccident examination of the airplane confirmed that fuel was present. The engine was rotated and compression was verified on all cylinders. The magnetos showed spark that was confirmed at all of the spark plug leads. No mechanical reason for the loss of engine power was found. At the time of the accident the temperature and dew point were 24 degrees C and 17 degrees C respectively. According to a carburetor icing probability chart, the temperature and dew point were in a range of susceptibility for moderate icing at cruise power settings and serious icing at descent power settings.