According to the pilot, while on a cross country flight he decided to descend and overfly a lake. While maneuvering over the lake with the setting sun at low level, the right main landing gear struck a marked power line, about 70 feet above the lake's surface; the right landing gear separated and broke an engine mount on the airplane. The pilot immediately turned the airplane toward a nearby airport and performed a forced landing. The left main landing gear collapsed on landing and the firewall sustained substantial damage. The pilot reported no mechanical malfunctions or failures with the airframe or engine that would have precluded normal operation. A witness stated that the power lines were marked by orange balls, while the pilot stated that the balls were red and dark. When asked how the accident could have been prevented, the pilot stated that yellow or white balls would have been easier to see.