Manatees have no natural predators in the wild but humans have played a large part in making all three species at risk of extinction. About half of West Indian manatee deaths are caused by humans, and most are due to boat collisions. Manatees are quite buoyant and use their horizontally placed diaphragm and breathing to control their buoyancy. This and their average speed of 3 to 5 miles per hour means that manatees are way too slow to escape from the path of a speeding boat.
In the Simpsons season 17 episode “Bonfire Of The Manatees” (Original air date: 9/11/2005) Homer gets into trouble over his football gambling debts and allows the Springfield Mafia to shoot a porno film in the house; Marge leaves for the beach—and encounters a marine biologist named Caleb (voiced by Alec Baldwin) who has dedicated his life to saving manatees.