Beavers have bounced back and are re-engineering the landscape in parts of Canada they occupied before they were almost wiped out by the fur trade over four centuries from 1600, said the man who found the world’s largest beaver dam in Wood Buffalo National Park, which straddles Alberta and the Northwest Territories.

“They’re invading their old territories in a remarkable way in Canada,” said Dutch-born landscape ecologist Jean Thie in 2010. “I found huge dams throughout Canada, and beaver colonies with up to 100 of them in a square kilometer.”

Construction of the gigantic dam, located in a virtually inaccessible part of the park about 190 kilometres (120 miles) northeast of Fort McMurray, Alberta, likely started in the mid-1970s, said Thie. “Several generations of beavers worked on it and it’s still growing.”

In 2007, he was looking at the latest satellite imagery of places he had examined via satellite in 1973 and 1974, when he was studying permafrost. As he looked over 1970s images taken by NASA’s Landsat satellite and compared them with the latest images from Google Earth, he noticed that in certain landscapes the evidence of beavers now was everywhere.

In particular, he noticed a belt about 1,100 miles long that extended into Wood Buffalo Park. Among the hundreds of beaver dams in this area, he found one that was 2,790 feet or about a half-mile long. The dam had created a 17-acre lake and the beaver lodge could be seen in the centre of the lake.

 A 652-meter structure in Three Forks in the US state of Montana previously held the record for world’s largest beaver dam.

A park spokesman said that when rangers flew over the forested marshlands in 2009, they found significant vegetation growing on the dam itself, suggesting it’s very old. The dam is visible in NASA satellite imagery from the 1990s.

While many beavers that have reestablished themselves globally are descended from beavers that were planted by wildlife biologists, that isn’t true of Wood Buffalo Park. Thie believes the beavers who built the dam are of original stock who were too remote to be hunted, says Yale Environment 360. 

Even now, it is so remote that only one person has trekked in to see it since that 2007 discovery. His story is told in the Yale Environment 360 article

Sources:

Deep in the Wilderness, the World’s Largest Beaver Dam Endures. Yale Environment 360, Dec. 11, 2023

The Longest Beaver Dam in the World EcoInformatics International, October 2007

Cover image: Rob Belanger, Parks Canada, in Yale Environment 360.