West Indian manatee, Trichechus manatus, at Three Sister's Springs off the Crystal River in Crystal River, Florida, USA. The West Indian Manatee is a large gray or brown aquatic mammal. Adults average about 10 feet long and weigh 1,000 pounds. They have no hind limbs, and their forelimbs are modified as flippers. Manatees inhabit both salt and fresh water of sufficient depth (1.5 meters to usually less than 6 meters) throughout their range.