Beaver dam in the Sawtooth National Forest, Idaho, USA

© Charles Knowles/Alam

Slowing the flow

Don't get distracted by the, admittedly striking, top half of today's photo. The postcard appeal of Idaho's Sawtooth Range – part of the Rocky Mountains - is undeniable, but we’re focused on the humble structure at the bottom. Beaver dams like this can be found from coast to coast in the United States and Canada, and now is the time of year when these industrious rodents set to work reinforcing their dams. Listening closely for trickles of running water, they patch compromised sections with logs and mud, securing their habitat for the winter.

And their efforts have important downstream effects: Beaver dams help to prevent floods by slowing water flows, and also filter out sediment to create cleaner streams and rivers. A stream in Canada's Wood Buffalo National Park, in Alberta, is said to be home to the world’s largest beaver dam, at more than half a mile long.