The river otter is a member of the weasel family and establishes a burrow close to the water's edge. The den typically has many tunnel openings, one of which generally allows the otter to enter and exit via the water. A den is also called a holt or couch. Female otters give birth in these underground burrows, producing litters of one to six young.
The newborn pup is cared for by the mother, father and older offspring. Female otters reach sexual maturity at approximately two years of age and males at approximately three years. After one month, the pup can leave the holt and after two months, it is able to swim. The pup lives with its family for approximately one year. Otters live up to 16 years.
Fish is a favoured food among the otters, but they also dine on amphibians, turtles, and crayfish. The northern river otter can weigh between 5.0 and 14 kg (11.0 and 31 lb) and is protected and insulated by a thick, water-repellent coat of fur.
River otters are very susceptible to environmental pollution, which is a factor in the continued decline of their numbers.