The West Indian manatee (Trichechus manatus), in the winter, moves to more temperate parts of Florida, such as the warm headwaters of the Crystal and Homosassa Rivers in central Florida or the tropical waters of southern Florida. When the air temperature rises to 50°F (10°C), it will wander back along the Gulf coast and up the Atlantic coast as far as Virginia. Long-range offshore migrations to the coast of Guyana and South America have been documented. In 1893, when the population of manatees in Florida was reduced to several thousand, the state gave it legal protection from being hunted or commercially exploited. However, many animals continue to be killed or injured by the encroachment of humans. Entrapment in locks and dams, collisions with barges and power boat propellers, and other man-made objects, cause at least 30 percent of the manatee deaths, which total 125 to 130 annually.