A beaver is a kind of large rodent. It is "semi-aquatic", meaning some of the time it lives in water, some of the time it lives on land. Beavers can only be found in North America and Europe. In Europe, they almost became extinct (died off), but they are returning. There are beavers living in the Elbe and Rhone rivers, as well as in Bavaria, Poland and Scandinavia. Beavers are known for building and keeping dams in rivers.