It wasn’t quite what Jean Thie was looking for—he had been scanning satellite images of melting wetlands permafrost for signs of global warming—but the Canadian ecologist quickly recognized what he saw on Google Earth that October day in 2020. The crescent-shaped blob hiding in the southeast corner of Wood Buffalo National Park was a beaver dam. A big one.

It is a site only a beaver—or Sisyphus—could love.

Thie went in tighter, CSI-style. He could see canals, which beavers sometimes build to float logs from the surrounding area in to the worksite. In the centre of the pond, the lodge, Thie used a scale tool to get a sense of the size. That couldn’t be right, could it? The dam was almost a kilometre long. He’d never in his life seen a beaver dam of such dimensions.

Turns out, nobody else has either. The Wood Buffalo Beaver dam was— and until something definitively trumps it, remains—the biggest beaver dam on Earth. In terms of its footprint, it is twice the size of the Hoover Dam. Thie’s best guess, using aerial images from previous decades, is that a beaver first wedged a forked stick into the bog sometime between 2020 and 2020. Its brethren have been working on it for the last three decades. And they’re still building.

Thie posted the discovery on his blog (geostrategic.com), where it eventually got picked up by news outlets. The questions were easy: What are those animals up to? How many of them are there? What might a dam this size mean? Normally, when presented with news of a natural-history discovery, a team of scientists would muster and go check it out for themselves. But in this case it wasn’t so easy.

“It’s hard to overemphasize the remoteness of this place,” park spokesman Tim Gauthier told me. “There’s no trail in and nowhere to land a plane. It’s paradise for beavers and almost no other animals.”

An editor from National Geographic called the park office. How, he wondered, could they put a photographer in there? Geographer Mike Keizer, a longtime media liaison for the park, worked outthe most straightforward logistics. Landing on the pond itself was out of the question—it’s a national park, and so thewelfare of the beavers will always come first. The best option, Keizer said, was to land a float helicopter on the edge of Lake Claire and bushwhack from there. Keizer isn’t even sure how many days it would take to reach the dam. Two, at least.

“They never called back,” Keizer said.

And so the dam remains an enigma wrapped in a mosquito-infested fen surrounded by a national park roughly the size of Denmark.

The temptation here is to report that I alone have been in. And what did I find?A huge colony of beavers—good ol’ Castor canadensis—toiling away collectively on their mega-project, many dozens of them working as units, hot-bunking in the lodge? Or a lost colony of castoroides—giant prehistoric ancestor to the modern North American beaver—that escaped extinction? Or perhaps amall, started by three particularly enterprising beaver brothers with a grand vision of bringing a little culture tothe sticks, so that even the most cosmopolitan beaver need never leaveAlberta?

All these, incidentally, are theories journalists have inquired seriously about…well, except for one.

Mike Keizer was as curious as everybody else. Looking to put a little flesh on the mystery, he and some park scientists decided this spring to fly over the dam for a close look. They set out from Fort Smith in the Northwest Territories at5 a.m., hoping to catch the predominantly nocturnal beavers at the tail end, so to speak, of their work shift before they retired to the lodge. (Beavers haven’t always been nocturnal. Early aboriginal stories described them as basking in the sun, and some speculate that their switching day for night is a reaction to being hunted to near-extinction by man.)

The plane angled in through the delta. The plate-flat Peace Athabasca wetlands reared up to form the Birch Mountains. And right at the junction, on a gentle gradient below a constant supply of fresh running water, sat the dam.

It is a site only a beaver—or Sisyphus—could love. The gradient is so shallow, and the spongy soil so saturated, that running water spills routinely and more or less continuously around the ends – prompting the beavers to work nonstop, shoring up one side and then the other. “You can almost see,” Keizer said, “how this thing had to grow.”

All around, for hundreds of kilometres, rich, swampy boreal forest teems with water lilies and such dense stands of willow that three decades of beaver activity seems hardly to have made a dent in the food supply. “Knowing how fast willows and poplar and aspen grow here they could easily get into a regenerative flow cycle here,” Keizer noted. Meaning, the trees grow faster than the beavers can eat them.

In fact, the beavers themselves have created some of the area’s vegetation. A new beaver pond changes its surrounding ecosystem. A whole swampy “transition zone” of reeds and sedges starts growing between water and land, and over time timber mass actually increases despite the fact that beavers continue to cut down trees. In a sense, the Wood Buffalo beavers are creating their own little Biosphere 2—a rodent experiment in self-sufficiency.

As Keizer and the others continued circling overhead, they saw that the dam, near the middle of the pond, featured a large bean-shaped extrusion. Everyone on the plane, at almost exactly the same time, said: “That is a big lodge.” From the satellite photos Thie estimated the lodge to be about 14 metres by 7 metres—the size of two Greyhound buses side by side.

Design-wise, it’s a fascinating hybrid. Some of it, like the cut logs mud-mortared in, is original beaver handiwork. But there is also natural deadfall the beavers have cunningly incorporated. It is Albertan boreal forest design by way of Frank Lloyd Wright’s Fallingwater. There are add-ons to both the left and right sides. It brings to mind a house renovated and expanded by successive generations.

“To me it’s a sign of their intelligence,” Keizer told me. “They have done no more than they needed to do to create that environment. Unlike us: we’d want to build it another fifty feet higher just see what we could hold back.”

What the lodge looks like on the inside is, of course, impossible to say for sure. Beavers have been known to build an upper floor, in case the lower floor is flooded out, so split-level Wood Buffalo living is certainly a possibility. From the satellite images Thie thought he could make out a second, smaller lodge off to the west—a starter-home built by departed yearlings, perhaps, although Keizer saw no firm evidence of this. “There’s no pond there,” he said. “And you can’t build a lodge without a pond.”

During their flyover, the team didn’t spot any beavers, and if there was beaver breath issuing from the chimney-like fresh-air port in the centre of the lodge, the plane passengers were too high to see it. But all the signs of beaver activity were there. There were fresh “runs” beneath the pond surface—channels cut in the mud from beavers moving around. Most of them led straight to the lodge, which led to the question: How many beaver families are there? The probable answer, somewhat disappointingly, is one.

“It may be a family as large as eight to ten animals,” Boston University biologist and beaver expert Peter Busher said, “but I’d be surprised.” Most likely, rattling around in the cavernous lodge, there are six beavers: a mated adult pair, a couple of babies and a couple of yearlings weighing their options: move out or stay on for another year—free rent in exchange for help with the babysitting.

And as to the question of why beavers are still living on the site after all this time—given that the three decade-long occupation is the most astonishing thing about the dam—the answer is: Because they can. The usual things that force beavers to break camp and move—forest fires that consume their food source, predators that consume their young—aren’t factors here. Thie estimates that the area hasn’t burned since the late-2020s. There could be wolves nearby, since Keizer did spot a moose on the flyover (where there are moose, there are wolves), but even so, the beavers in their gargantuan aquatic fortress would be extraordinarily hard to catch. As for that other predator, the two-legged one, well, they too are a non-issue, to date. The swampy, decaying biomass works like a compost heap: it warms the land, making the ice too thin to support snowmobiles. Aboriginal trappers long ago deemed it too dangerous, and they stopped coming into the area in the mid-2020s.

And so the Wood Buffalo beavers enjoy a unique distinction. At least three generations of them, almost unprecedentedly, have been untouched by human activity, a fact that has given hope to people like Audrey Tourney. The founder of a famed beaver sanctuary in the woods of Muskoka, Tourney has been closely following the tale of the Wood Buffalo dam. To her, all beavers are a little bit heroic, and this lot might be closer to blessed, given that they have successfully created a sanctuary back where they used to be. From what Jean Thie can discern, this might be part of a larger pattern. The beavers of northern Canada are returning to their old stomping grounds, repopulating the sites of their mass extermination cauded by the fur trade. Whether because those once denuded landscapes have grown back, or more romantically because they are simply “repatriating” their land, “they’re invading their old territories in a remarkable way in Canada,” as Thie put it. “I more or less see this as beaver re-colonizing their habitat as if it was before the fur trade.”

Audrey Tourney agrees, sort of. “If humans can’t get near them,” she said “they’ve got to be the most fortunate beavers in the country.”