North American river otters are semiaquatic mammals. Like most predators, they prey upon the most readily accessible species. Fish is a favored food among the otters, but they also consume various amphibians (such as frogs), turtles, and crayfish.
River otters characteristically approach within a few feet of a boat or a person on shore because they’re near-sighted, a consequence of vision adapted for underwater sight.
Otters swim by quadrupedal paddling, forelimb paddling, alternate hind-limb paddling, simultaneous hind-limb paddling, or body and tail dorsoventral undulation. The tail, which is stout and larger in surface area than the limbs, is used for stability while swimming and for short bursts of rapid propulsion. While swimming at the surface, the dorsal portion of the river otter’s head, including nostrils, ears, and eyes, is exposed above water. It must remain in motion to maintain its position at the surface.