The beaver—buck-toothed, paddle-tailed and famously industrious—has been reshaping freshwater landscapes for millions of years. With their iron-reinforced orange incisors, these skilled rodents cut down trees and build dams that slow the flow of water, improve its quality and create wetlands that support a remarkable diversity of life. Their sturdy lodges, made of branches and mud, have underwater entrances that protect them from predators and keep their families safe.