Beavers usually cut the wood away around a tree trunk, but they may cut through the trunk from only one side. Building dams and canals. A beaver cuts down trees even if it has no place to build a dam or a lodge, and even if it has more than enough food. A whole beaver family, and sometimes beavers from other families, may join in building a dam. Beaver dams are made of logs, branches, and rocks plastered together with mud.
Beavers use mud and stones for the base of a dam.
Then they add brush and log poles. They strengthen the dam by placing the poles so that the tips lean in the same direction as the water flows. The beavers plaster the tops and sides of the poles with more mud, stones, and wet plants. They do most of this work with their front teeth and front paws. They bring mud from the river bottom by holding it against their chests with their front paws.