Manatees are enormous - adults weigh between 400 and 600 kilograms and can be up to 4 metres long. Despite their size, they are completely harmless. They have no teeth designed for meat; their big, flat teeth are only for grinding up sea grass.
Manatees breathe air just like we do and must come to the surface every few minutes to take a breath. They often float just below the surface with their nostrils poking out - if you are in a boat and look carefully, you might spot the two tiny nostrils breaking the water.
A manatee can eat a tenth of its own body weight in sea grass every single day. This grazing actually helps keep sea grass beds healthy, a bit like how mowing a lawn keeps it tidy. Healthy sea grass beds are important homes for fish, crabs and sea horses.
Manatees are related to elephants - scientists believe they share a common ancestor from millions of years ago. If you look at a manatee's flipper very closely, you can even see tiny fingernails, just like an elephant's toes.