Largest beaver dam discovered from space

In a remote corner of northern Alberta, Canadian beavers have built the world’s largest dam, proving once and for all they are worthy of their status as a national symbol.

The roughly 850-metre dam — located at the southern edge of Wood Buffalo National Park, about 200 kilometres northeast of Fort McMurray — is believed to be the work of several generations of beavers.

The massive structure captured international attention this week, more than two years after it was first discovered by an Ottawa ecologist surveying the area through satellite imagery.

The dam is so big, it can be seen from space.

"I think it’s great that our Canadian icon is bringing attention to our national parks," park spokesperson Mike Keizer told CTV.ca, a reference to the beaver’s role as a national emblem.

But the dam won’t become a tourist attraction, despite the buzz. The wood-and-mud formation stands in an isolated spot, a multiple-day paddle and hike through un-trailed areas – so far that even rangers only view it from the air, Keizer said.

Environmental scientist Jean Thie found the structure in Oct. 2007 while using Google Earth to monitor permafrost in the country’s boreal and sub-arctic regions. The discovery led to a hobby cataloguing beaver dams and their size.

The now-famous dam appears on aerial photos as far back as 1975, said Thie, president of EcoInformatics International Inc., a consulting firm for science and natural resource management organizations.

The area boasts a few other impressive dams ranging between 300 and 500 metres, Thie said. Most beaver dams stretch less than 100 metres.

Thie’s research on the dam caught the eye of British journalists, who approached park staff to schedule a visit in the winter of 2007. No one at the park knew the dam existed.

Rangers flew over the site the following summer to see the dam for themselves, Keizer said.

"It doesn’t look like much," he said. "It looks like a bog against a dense forest."

There’s also a possibility beavers didn’t do all the construction themselves. Some of the natural deadfall caused by spring flooding may have provided some of the lumber, leaving the beavers to plug the holes, Keizer said.

"You can’t tell from the air," he said, noting the dam is well covered in vegetation.

The park is part of what Thie calls Canada’s "beaver belt," a zone that spans Manitoba’s Riding Mountain National Park through Saskatchewan, on to northern Alberta and northeast British Columbia.

"In some parts of Alberta and Saskatchewan, some dams are quite amazing," he said.

That particular stretch of Wood Buffalo park is flat, so the beavers had to build a long dam to block the wetland waters, the researcher said.

It could continue to expand in the next decade if it annexes two smaller adjacent dams, he said.

Beavers build dams to create deeper ponds that provide underwater food storage and secure access to their lodges. The structures comprise layers upon layers of sticks, rocks and mud, and can stand up to great water pressure.





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