The pilot said that prior to takeoff he walked a large portion of the frozen lake to check its suitability for use. He said although recent rain left about 2 inches of standing water on the ice-covered surface of the lake, he felt the lake was suitable for takeoff. The pilot said that during the takeoff roll, the tail lifted and transferred the weight of the airplane to the main landing gear. The main wheels then encountered water deeper than he expected, and the airplane nosed over. The airplane received wing and lift strut damage during the accident.