The pilot stated that he departed about 0620 from his private property and flew to his friend’s private grass strip. During short final approach, the pilot permitted the airplane’s airspeed to get slow and the altitude to get low. He increased the engine power; however, the pilot stated the engine did not “seem” to immediately respond. Although the pilot tried to stretch the glide to reach the intended grass strip, the airplane skimmed the river water in front of the strip and the airplane’s nose section impacted with the riverbank. The airplane flipped over and came to rest inverted at the beginning of the grass strip, incurring substantial damage to the vertical empennage section. The pilot stated the airplane was in excellent mechanical condition and he did not experience any mechanical problems during the flight. A review of the pilot’s certification by the Federal Aviation Administration inspector revealed that his last medical was in February of 2007, and was expired.