Beaver, Germany (© Andyworks/Getty Images)

International Beaver Day, celebrated on 7 April, recognises a hardworking little engineer quietly building a better world—one stick at a time. 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.