Canada’s Wood Buffalo National Park, the country's largest, hides the biggest beaver dam ever recorded. Deep inside the park, far from roads and towns, this dam stretches about 775 metres, almost as long as seven football fields. It covers around 70,000 square metres and holds back approximately 70,000 cubic metres of water — the same as over 90,000 dump truck loads. The dam is so massive, it was first spotted not on the ground but from satellite images in 2007. NASA’s photos revealed it didn’t exist before 1980, meaning beavers took around 40 years to build it piece by piece. Reaching it on foot is tough; dense forests and wetlands surround the area, so most people who have seen it flew over in private planes. Beavers are known as nature’s engineers, shaping lands by building dams to create ponds. This giant dam helps slow water flows and supports a rich ecosystem in the park, home to wood bison and whooping cranes. Quiet and hidden, the beaver dam keeps working, changing its part of the park little by little, even if most people will never see it up close.