A "beaver dam" is a structure built by beavers using branches, logs, and mud to create a barrier across a river or stream. It forms a pond and provides shelter and protection for beavers. Full definition
It's common for beaver dams in Canada to reach 500 metres in length. (cbc.ca)
With Battle Creek providing the water to several ponds created by beaver dams, and several views of Puget Sound, Camano Island and the Olympic Mountains. (petesgrillandpizza.com)
Later, they visited a community affected by a large beaver dam and surveyed residents on possible solutions for how humans and beavers can coexist. (heliosns.org)