North American river otters can usually be found alone or in a pair. However, they are rather social animals and are known to be social within their groups. They live in dens that are located near streams, rivers, and other water sources. They use their scent to mark territories and communicate their sexual state.
They are excellent swimmers and usually will slowly move along the surface of the water by dog paddling with their webbed limbs. When swimming fast however, they will use their tails to thrust themselves. Their forelimbs stay tucked to their chest except when steering. They can also remain submerged underwater for 6-8 minutes at a time while trying to catch fish.
A third eyelid, or nictitating membrane, protects an otter’s eye and allows them to see while swimming, similar to a pair of goggles.