North American river otters are semi-aquatic mammals, with long, streamlined bodies, thick tapered tails, and short legs. They have wide, rounded heads, small ears, and nostrils that can be closed underwater.The fur is dark brown to almost black above and a lighter color ventrally. The throat and cheeks are usually a golden brown. The fur is dense and soft, effectively insulating these animals in water. The feet have claws and are completely webbed. Body length ranges from 889 to 1300 mm and tail length from 300 to 507 mm.North American river otters are found anywhere there is a permanent food supply and easy access to water. They can live in freshwater and coastal marine habitats, including rivers, lakes, marshes, swamps, and estuaries. North American river otters seem to be sensitive to pollution and disappear from areas with polluted waters. North American river otters build dens in the burrows of other mammals, in natural hollows, such as under a log, or in river banks. Dens have underwater entrances and a tunnel leading to a nest chamber that is lined with leaves, grass, moss, bark, and hair. Males and females do not associate except during the mating season. Males often breed with several females, probably those whose home ranges overlap with their own. Lontra canadensis individuals live alone or in family groups, typically females and their young. They are known as playful animals, exhibiting behaviors such as mud/snow sliding, burrowing through the snow, and waterplay. Many "play" activities actually serve a purpose. Some are used to strengthen social bonds, to practice hunting techniques, and to scent mark.North American river otters communicate in a variety of ways. They vocalize with whistles, growls, chuckles, and screams. They also scent mark using paired scent glands near the base of their tails or by urinating/defecating on vegetation within their home range.North American river otters eat mainly aquatic organisms such as amphibians, fish, turtles, crayfish, crabs, and other invertebrates. Birds, their eggs, and small terrestrial mammals are also eaten on occasion. They sometimes eat aquatic plants.
Source: Lontra canadensis Northern River Otter, Animal Diversity Web, University of Michigan Museum of Zoology