On October 11, 2006, about 1200 eastern daylight time, a Hughes OH-6A, N810SB, registered to and operated by individual, as a Title 14 CFR Part 91 personal flight, ditched in the bay near the shoreline of Ocean Reef Club, Key Largo, Florida. Visual meteorological conditions prevailed and no flight plan was filed. The commercial-rated pilot and one passenger were not injured, and the helicopter incurred substantial damage. The flight originated from Ocean Reef Club Airport, Key Largo, Florida, earlier that day, about 1100. The pilot state that he maneuvered the helicopter to the southeast corner of Ocean Reef so the passenger, a photographer, could take photos of a house at the water's edge. The helicopter was in a steady hover over the water with the nose toward the north. The winds were from his left, from the west, at about 10 knots. There were no abnormalities noted with the helicopter's power. He increased left pedal to bring the nose of the helicopter more into the wind to smooth out the aircraft from the effects of the winds on the tail rotor. Suddenly the helicopter started an un-commanded turn to the right. He applied full left pedal, reduced collective, and initiated forward flight. The helicopter continued the right turn. After several rotations and close to the water he initiated an auto-rotation from about 10 feet above the water. He used collective to cushion the contact with the water. The helicopter came to rest on its right side in about 7 feet of water. The passenger stated that while doing aerial photography at about 150 feet above sea level, the helicopter started spinning and spiraling down. They hit the water soon after. A representative for the helicopter's manufacture, with FAA oversight, examined the helicopter. No abnormalities were found with the helicopter's flight control system. All damage noted to the helicopter was consistent with a water impact. The FAA Aeronautical Handbook\FAA-H-8083-21-Rotorcraft Flying Handbook \Chapter 11\ Helicopter Emergencies\Systems Malfunctions\Unanticipated Yaw\Loss of Tail Rotor Effectiveness states that an unanticipated yaw is the occurrence of an uncommanded yaw rate that does not subside of its own accord and, which, if not corrected, can result in the loss of helicopter control. This uncommanded yaw rate is referred to as loss of tail rotor effectiveness (LTE) and is not related to an equipment or maintenance malfunction and may occur in all single-rotor helicopters at airspeeds less than 30 knots. It is the result of the tail rotor not providing adequate thrust to maintain directional control, and is usually caused by either certain wind azimuths (directions) while hovering, or by an insufficient tail rotor thrust for a given power setting at higher altitudes.