In a remarkable example of natural engineering, beavers constructed a dam that filtered polluted water flowing into a protected area—achieving what local authorities had spent seven years planning but had not yet implemented. The animals unknowingly completed the project for free. The beaver dam slowed water flow, trapped sediment, and prevented contaminated runoff from spreading downstream. When officials inspected the site, they realized the dam accomplished the same environmental goals as a p

Building a proper dam takes more than a good pair of teeth. Beavers are basically designed for the job. | National Geographic TV