Beaver dams can last for generations.

If there’s one thing beavers love, it’s building dams — and they’re damn good at it. These makeshift structures, which they build to create deep, calm water where they’re safe to eat, sleep, and generally enjoy their day safe from predators, can be maintained and even expanded over several generations. Doing so requires near-constant maintenance in order to keep the water level steady, and if a dam is successful enough it will eventually have to be expanded in order to extend the beavers’ feeding area.

The world’s largest dam, located in Canada’s Wood Buffalo National Park, is more than 2,700 feet long. It’s believed to have been built sometime after 1975 and is so remote that only one person has made the trek to visit it.