Alberta’s busiest builders

The biggest dam ever redefines the limits of beaver architecture
Stephen J. Krasemann / Getty Images

Here’s a complete list of the equipment Jean Thie used to discover the world’s longest beaver dam: 1. Google Earth. 2. His brain. One of these he was born with; the other’s a free download. His record, which came to international attention this month by means of one of those curious Internet epidemics, stands waiting to be broken. If you have a computer and a knowledge of beaver habitat, you could break it yourself. He seems a sporting fellow, and would probably rather like it if you did.

Thie is an expert in forests and wetlands, and in the use of computers and aerial imaging in environmental management; his Ecoinformatics International consultancy is based in Ottawa. In 2007, he was studying the effect of climate change on permafrost when he found himself becoming increasingly curious about the large beaver dams he was spotting on Google Earth in Canada’s boreal zone.

“I gradually switched my approach to studying landscapes with beaver in them,” he says. “As a landscape ecologist I became interested in the way that beavers were re-engineering, really reconquering their previous territory.” His quest, moving westward from Hudson Bay, led him to the south margin of Wood Buffalo National Park, the Switzerland-sized wildlife preserve that straddles the Alberta-N.W.T. border. By now he was actively hunting for a record-breaking dam, and he correctly anticipated that the park, protected by both nature and the law, held promise. (Only a handful of licensed Aboriginal diehards still trap within its boundaries.)

Thie discovered a startling constellation of beaver dams in a gently sloping, boggy zone near the park’s otherwise unimpressive Birch Mountain range of hills. The classic, familiar beaver dam on a stream or river can reach a height of four metres or more. But in “alluvial fan” areas where water flows slowly over broad stretches of sediment, rather than forming channels, beavers will build long, low crescent-shaped dams and just keep going until they have created a pool large enough to protect a lodge from predators. The largest dam in Thie’s Birch Mountain beaver zone is a stunning 850 m long—long enough that you could lay the CN Tower (553 m) next to it and still come up short by three football fields. It is 200 m longer than the previous record holder, and has redefined the known limits of beaver architecture.

Thie announced the discovery quietly on the Web, and the staff of the park didn’t learn of it until a BBC documentary crew called in 2008 to inquire about access to the world’s largest beaver dam. “I had to tell them, ‘Sure, but where is it?’ ” says Parks Canada spokesman Mike Keizer. The story has expanded by fits and starts ever since, going viral via the BBC World Service on May 8 and culminating in a brief comedy bit on Ellen Degeneres’s daytime talk show on May 12. Many news producers were drawn to the misleading claim that the dam “can be seen from space,” which it can, but only in the sense that, like your car or your house, it can be photographed from there.

Thie has already fielded dozens of calls and emails about his find. One came from a former surveyor in Alberta’s north who says he encountered a 3,000-foot-long dam in the late ’60s; he resisted telling his story for decades, since he knew there was no scientific evidence such a thing could exist, and has greeted news of a confirmed 2,800-foot specimen with rapturous relief.

The record-setting dam is perhaps more impressive in satellite pictures than it seems from a helicopter. There are at least two lodges in the pond formed by it, suggesting that the single dam may have begun as two separate ones which eventually became conjoined. The Big One would probably be an awesome spectacle from the ground, but reaching it on foot, even from the nearest conceivable location for a chopper landing, would be a daunting challenge for the most experienced trailblazer. One of the air carriers based in Ft. Smith, N.W.T., the sole gateway to the park for much of the year, is already making plans to add the dam to aerial sightseeing tours.

It has not been established that the dam complex is currently inhabited, and since beavers are mostly nocturnal, it will be hard to settle the matter without a terrestrial expedition. Keizer flew over the dam on the morning of May 15, and he believes he saw signs of occupation. “Looking from the air, the water is clear enough that you can see straight through to the bottom. There are grooves in the mud that could have been made by beavers recently.”

The dam was probably a multi-generational project, though certainly never one with more than a handful of beavers working on it at any time. Beavers live for about four or five years on average and mate for life. The vulnerable kits normally arrive three to five at a time, but their numbers will vary according to the availability of food and space. They are ready to help with construction between the ages of 12 and 24 months, but eventually, as with humans, breeding pairs will drive off their own children from the home lodge to shift for themselves. Thie has established, using images from NASA and the National Air Photo Library, that the big dam did not exist at all in 1975, but had attained roughly its current size by 1990. There is a small dam, almost invisible on Google Earth, just 100 or so metres west of the big one; its builders are probably exiled family members, and it might ultimately connect to the main dam, increasing the size of the whole super-beaver-plex still further.

The dam brings welcome attention to Wood Buffalo National Park at a difficult time for its defining celebrity species: the ever-struggling whooping crane and the controversial, disease-ridden herd of free-ranging wood bison. Our national rodent, by contrast, will always be good at attracting an audience. Before Darwin accustomed us to thinking of animals as automata programmed by evolutionary processes, naturalists took the beaver seriously as a mute partner of humankind, comparable to us in reasoning, planning ability, and dignity. So we still instinctively regard him when we’re reminded that his engineering rivals our own in scale and functionality.