The pilot of a Schweizer 269C helicopter was conducting a non-revenue sightseeing flight, looking for alligators, and he entered an out-of-ground-effect hover at 50-70 feet above ground level. He hovered the helicopter into the wind, which he based on the water conditions. After hovering for about 5 seconds, the pilot pitched forward on the cyclic and raised collective. The helicopter then entered an uncommanded right yaw. The pilot immediately lowered the collective, applied forward cyclic and left anti-torque pedal; however the yaw continued. The helicopter completed at least eight 360-degree turns to the right, as he leveled the helicopter, and raised the collective. The helicopter subsequently landed in the about 2 feet of water and came to rest upright, without injuries or damage to any property. The helicopter sustained damage to the landing skids and cross tubes. The pilot believed he experienced a loss of tail rotor authority, and he did not feel any vibration in the anti-torque pedals. He remarked that the nearby trees could have changed the wind direction. The reported wind near the accident site, about the time of the accident, was from 310 degrees at 7 knots. Postaccident examination of the helicopter did not reveal any preimpact mechanical malfunctions.