North American River Otter

North American river otters are found anywhere there is a permanent food supply and easy access to water in the UP. . They can live in freshwater and coastal marine habitats, including rivers, lakes, marshes, swamps, and estuaries. River otters can tolerate a variety of environments, including the cold winter of the Upper Peninsula. 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.

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 vibrissae are long and thick, reflecting their importance in sensory perception. 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. Weight ranges from 5 to 14 kg. Males average larger than females in all measurements.