An excellent swimmer, this large rodent spends much of its life in water and has webbed hind feet and a long, naked, vertically flattened tail which it uses as a rudder. It feeds on aquatic and land vegetation and occasionally on some mussels, frogs, and fish. It usually digs a burrow in the bank of a river, but where conditions permit, it builds a lodge from plant debris in shallow water and inside it constructs a dry sleeping platform above water level. The lodge may shelter as many as 10 animals. At the onset of the breeding season, the muskrats' groin glands enlarge and produce a musky secretion, believed to attract male and female to one another. They breed from April to August in the north, and throughout the winter in the south of their range. Two or three litters of 3 to 4 young are born after a gestation of 29 or 30 days.