Longest beaver dam
Wood Buffalo National Park in Alberta
Canada (Wood Buffalo National Park)

The longest beaver dam in the world measures some 850 m (2,788 ft) long. It is located in the far south of Wood Buffalo National Park in Alberta, Canada. This massive structure, which is more than twice the length of the Hoover Dam, was first spotted in 2007 by researcher Jean Thie (Canada) while studying satellite photos of the region. Its existence was confirmed by rangers from Parks Canada, who took pictures from a helicopter in May 2010. After reviewing old satellite and aerial photos, Thie concluded that the dam is the work of several generations of beavers, who have probably been working at the site since the mid-1970s.

The beaver dam passed unnoticed for such a long time because it is located around 80 km from the nearest human settlement – Fort Chipewyan – deep within the wetlands that lie between the Peace Athabasca Delta and the Birch Mountain Highlands. It wasn't visited by a human until September 2014, when American adventurer Rob Mark trekked some 200 km through what the national park's spokesman described as "incredibly inhospitable territory" battling giant mosquitos and bad weather to reach the dam.