Beaver's outer hair is a dark chestnut brown. Usually their heads and underparts are slightly lighter than the rest of the body. This is not the case with the black subspecies of beaver. The two incisors in each jaw grow continuously as they are worn away. Beavers chewing force is 80 kg.
Family groups consist of two adults, several two year olds and the young of the current year.
They mate first at about three years old. Gestation 128 days. Mother carries the kits in her mouth supported on her front legs while walking upright on her hind legs and tail. Young leave or are forced out of the colony by two years. Large lodges may have several family groups.