One of two species of large, mainly nocturnal, highly social, semiaquatic rodents, the Eurasian (Castor fiber) and North American (C. canadensis) beavers. Beavers fell riverside trees, using the wood together with mud and stones to construct dams in small rivers creating a lake, and to build a lodge in the centre of the lake, with an entrance below the surface, where they live in colonies, protected from predators by the water. They feed on wood and other plant material.