Manatees are quite agile and maneuver well under water.
Florida manatees have been clocked swimming at speeds up to 24 kph (15 mph) for short bursts, but usually cruise about 3 to 10 kph (2-6 mph) or less.
Although manatees are excellent swimmers, the deepest an individual has been seen diving is 10 m (33 ft.). They normally feed no deeper than about 3 m (10 ft.) below the surface of the water.
All marine mammals have special physiological adaptations for diving. These adaptations enable a manatee to conserve oxygen while under water.
Manatees, like other marine mammals, have a slower heart rate while diving.
In contrast to whales and dolphins, manatees are not deep-diving marine mammals. Therefore, manatees' muscles do not contain the high concentrations of the oxygen-binding protein myoglobin that is typical of other marine mammals
Studies show that manatees renew about 90% of the air in their lungs in a single breath (humans renew only about 17%).
While resting, manatees can stay submerged for as long as 20 minutes, although the average interval between breaths for resting is two to three minutes. More active and smaller manatees breathe more often.