In case you always wondered. this appeared on animal planet last year and just dropped on youtube yesterday.
Yellowstone is changing. While many recognize this landscape for its towering peaks and thermal wonders, the true lifeblood of the region is moving beneath the surface. For centuries, the rivers and streams of the American West were maintained by a master architect that was nearly hunted to extinction. Today, the balance of the entire ecosystem rests on the shoulders of the beaver. This documentary, hosted by Dennis Quaid, follows the journey of a beaver family as they engineer survival in a world of plunging temperatures and dwindling water. By mimicking these natural engineers, conservationists are finding ways to combat drought and restore the vibrant, verdant valleys that Lewis and Clark witnessed over two centuries ago.
