This imposing rodent has a sleek, streamlined appearance, well suited to its aquatic habits. Its partially webbed hind feet enable it to perform complex maneuvers in the water. It feeds on small fish, frogs, crustaceans, and water birds which it pursues and captures. Catches are often taken to a special food store for later consumption. In the south of their range, water rats breed in early spring, producing a litter of 4 or 5 young; farther north they may breed all year round.