The pilot departed, conducted a touch-and-go at one airport, landed at another, and then flew north to a third airport, where another touch-and-go was conducted. The airplane then headed south towards the home airport, and the pilot descended to low level and followed a river for a portion of that flight leg. The pilot reported that the conditions were turbulent for most of the day, but during that low-altitude leg, the airplane behavior seemed abnormal. While still airborne, a passenger observed that the brake line that was attached to the right main landing gear strut was severed. As a result, the pilot conducted a precautionary landing at a nearby airport. The pilot and passengers observed multiple damage sites on the airplane, but since no one was present at that airport, they reboarded and departed for the home airport, where an uneventful landing was made. Investigation revealed that the airplane struck and severed one of several electrical power lines, which spanned the river. Those lines were strung between two poles, one on each side of the river. Both poles were set back from the river edge, and the west pole was situated in a loose stand of trees. The approximate wire span was 464 feet, and the wire height at mid river was approximately 30 to 40 feet above the water. Airplane damage from the wire strike included the propeller, cowling, exhaust stack, right wing (multiple places), right wing strut, right main gear brake line, right landing gear wheel fairing, right fuselage, and vertical stabilizer. In addition, the rear window was punctured. The pilot stated that he did not see any wires, and that he was not aware of the wire strike until he examined the airplane after the precautionary landing. Neither the pilot nor the passengers incurred any injuries.