Why are manatees in danger of becoming extinct?

Three reasons that Manatees are endangered is mainly because their habitat(Beds of sea grass, Wetlands, Mangroves) is being destroyed or drained for human population, but also because of water's becoming polluted which poisons them and the food they eat. Also because motorboats that come in Manatee habitat can injure or kill Manatee's with their propellors.