The student pilot stated he had practiced a simulated loss of engine power to a field near a river. After finishing the practice approach, witnesses observed the airplane flying north to south about 30 feet above the river. They observed the airplane climb and fly over a bridge, which spaned a river. The airplane then descended and hit power lines that crossed over the river. The airplane came to rest in the river about one mile south of the bridge. Portions of the horizontal stabilizer and the wing had separated from the fuselage. The pilot was seriously injured. An examination of the airplane revealed no anomalies.