Manatees are primarily herbivores. They feed on a wide variety of submerged, emergent, floating, and shoreline vegetation.

Manatees in Florida feed on more than 60 species of plants including turtle grass, manatee grass, shoal grass, mangrove leaves, various algae, water hyacinth, acorns, and hydrilla.

In Sierra Leone, Africa, the West African manatee is considered a pest because they consume fields of planted rice.

Manatees have occasionally been seen to eat foods other than plants. Antillean manatees have been known to eat fish from nets and West African manatees have been known to eat clams (Reynolds and Odell, 1991).

Manatees consume about 4% to 9% (15 to 49 kg or 32-108 lb. for an average adult manatee) of their body weight in wet vegetation daily.

Some Amazonian manatees living in deep bodies of water apparently fast during dry seasons (November and December) when water levels drop as much as 9 to 15 m (30-50 ft.), eliminating their access to vegetation.

Because manatees have a very low metabolic rate, it is speculated that Amazonian manatees are able to fast for up to seven months if necessary (O'Shea, 1994).

Manatees feed off the bottom, in the water column, and at the surface. They have been known to crop overhanging branches, consume acorns, and haul themselves partially out of the water to eat bank vegetation including the leaves of mangrove trees.

Manatees use their front flippers and large, flexible lips to manipulate vegetation.

Horny, ridged pads at the front of a manatee's palate (roof of the mouth) and lower jaw break vegetation into smaller pieces. Behind the pads, molars grind the food.

Both the West Indian and West African manatees may require a source of fresh water for drinking. Manatees have been seen drinking fresh water from hoses, sewage outfalls, culverts, and also congregating at river mouths. Most scientists agree that manatees must periodically have access to fresh water.