At approximately 0340 Eastern time, the helicopter was substantially damaged when it impacted a lake while maneuvering. The solo private pilot was not injured. Night visual conditions prevailed. After returning from a cross-country flight, the pilot took off in the helicopter to build night time and conduct a night landing. While maneuvering to return to the airport, the pilot saw the clutch actuator light illuminate and remain illuminated for nine seconds. The pilot reached for the circuit breaker box under the passenger seat and then felt “light in the seat.” The helicopter was rapidly descending, and he pulled up on the collective to arrest the descent. After pulling collective, he received a low rotor rpm horn and then observed the surface of the lake reflecting the moonlight about 50 feet below the helicopter, as it continued to descend. The pilot pulled collective to soften the impact and the helicopter came to rest in the lake. The pilot egressed the helicopter and swam to shore.