On June 12, 2001, at 1410 eastern daylight time, an amateur-built Giackino Exec 162F helicopter, N556DG, piloted by a private pilot, sustained substantial damage when it impacted the water while maneuvering near Manistique, Michigan. The aircraft came to rest in the Manistique River. The pilot and his one passenger were not injured. The flight was operating under the provisions of 14 CFR Part 91 and was not on a flight plan. The local flight departed from the Schoolcraft County Airport, Manistique, Michigan at 1340. The pilot reported that he was participating in a search for lost hunters in the area of Manistique, Michigan. He said that his flight pattern was to follow the Manistique river. He said that during the flight at about 50 feet AGL, he heard a sound that sounded like squealing of belts coming from the engine compartment. He said that the rotor speed began to slowly drop and he was unable to maintain rotor speed even after adding additional engine speed. The pilot executed a forced landing into the river. The pilot reported that there was dense forest to the left and people and vehicles to the right of his flight path. A postaccident examination of the helicopter was performed. The main rotor drive belts were found to be contaminated with a liquid. The pilot reported that the liquid was possibly engine coolant.