**Description:** A medium-sized, semi-aquatic rodent with dark, waterproof fur and a vertically flattened tail used as a rudder.
**Size & Weight:** 16–25 inches long. Weighs 2–4 lbs.
**Sexual Dimorphism:** Males and females are similar in size and appearance.
**Behavior:** Highly aquatic; they can swim backwards and forwards with ease. They dig burrows into riverbanks or build "push-ups" from vegetation.
**Habitat:** Common in marshes, beaver ponds, and the slow backwaters of the Allegheny River.