A dam is a barrier that stops the flow of water and forms a pond or lake. These new ponds make it easier for beavers to access trees found along the shoreline. A mating pair of beavers will usually set out to find a stream where they can build a dam. They collect logs and branches in a pile to create the dam and then use grass and mud to fill in the spaces between the branches. Eventually the water will pool up on one side of the dam to form a pond.
Beavers live in shelters called lodges.
Beavers start working on their lodges in the fall. Some beavers build in existing lakes while others build in the newly formed ponds that they made with the dams. The lodges must be ready by winter to shelter the beavers away from hungry predators such as wolves, foxes, and otters. Lodges are usually cone shaped with underwater entrances and are built along the shore. The beavers build from the inside out using mud, grass, and branches.