This stocky, muscular, amphibious member of the weasel family is distributed throughout most of North America, except the Far North. They attain a maximum length of about 1.4 m (4.5 ft.) and a weight of about 13.5 kg (30 lb.). Northern river otters have thick lustrous fur.

Wary in the wild, they are, nonetheless, sociable, docile, playful animals and easily domesticated. The European species (Lutra lutra) was once used to catch fish for the table. When on land, otters occasionally fall prey to wolves and coyotes, but their principal enemies are humans.

They prefer life on the shores of deep, clear rivers, lakes, large marshes and ocean bays. Their diet consists mainly of fish, but they also eat insects, frogs, and sometimes, small mammals such as muskrats. Primarily nocturnal, otters remain active year round.