This is a large, grayish-brown, stout-bodied rodent. Weights are from less than 12 to over 20 pounds. The total length can be up to 3-1/4 feet in length. The first 3 toes of the hind foot are webbed. This species is sexually mature at 5–6 months, and breed throughout the year. Two to three litters of 2–11 young are born each year. They build burrows, and winter nesting platforms 20–30 inches wide and 6–9 inches above the water. They also build simple nests in vegetation. Burrowing and burrow occupancy may be limited to the coldest part of the winter. This species is nocturnal and is not native to Virginia. They are limited to water, and aquatic vegetation and are spreading throughout the state somewhat at the expense of the muskrat. The life span average in the wild is 4–4-1/2 years (maximum 5 years, 11 months).
They are found in the eastern 1/4 to 1/3 of the state. This species thrives in fresh or brackish marshes where abundant vegetation is available for food.
This species is strictly herbivorous, and not too particular in selecting its menu. Food is limited to succulent and soft portions of shoots and tubers, coarse and floating leaves. The roots are the most important part of the diet (except in April-mostly stems). They eat at “feeding stations” and feed on nearly every kind of aquatic plant available.