Lack of freshwater undoubtedly account for low incidence of manatees in the Florida Keys and Bahamas. Research locally has indicated that manatees sense impending cold weather and head up stream to the Caloosahatchee Power Plant to prevent cold water shock. The outflow from the power plant is sufficiently warm enough to protect the manatees from the cold. The dilemma is no food is available in that vicinity, since manatees have over grazed the area. Manatees have even been seen crawling half way out of the water to be able to graze on mangrove leaves in such areas.
Manatees particularly enjoy grazing on submerged vascular plants.
That is, plants that have roots, stems, leaves and flowers in contrast to the simple structure of algae. Ironically, an exotic plant, the water hyacinth, is one of their favorite foods. The hyacinth, like many exotic, noxious weeds, have overgrown many portions of Florida's fresh waterways. Most of these sea grasses grow best in the shallow waters of the estuary. Fast moving boats traveling over these grass flats leave little opportunity for a manatee to take evasive action when its feeding in waters less than five feet deep.