Dam That's Big!

Wood Buffalo National Park of Canada is the largest park in Canada's system of National Parks and the 2nd largest protected area in the world, at 44, 807 square kilometres. It is also home to the world's largest.....beaver dam. Seriously.

The dam is, apparently, about one and a half CN Towers in length, ~850 metres or 2,800 feet long. The product of several generations of beavers, the dam blows past the old record of a dam 652 metres long in Three Forks, Montana.
Beaver dams are unusual in that they can be seen from space--like the Great Wall or the Pyramids at Giza. Canadian ecologist Jean Thie said Wednesday he used satellite imagery and Google Earth software to locate the dam, which is about 850 meters (2,800 feet) long on the southern edge of Wood Buffalo National Park.

Beaver can cut down as many as 200 trees a year, and generally build dams between 10 and 100 metres long. When such dams are near human development, the dams are usually destroyed and the beavers caught and transported to little beaver penal colonies new areas away from humans. These beaver, well away from people, have been free to reshape the environment as they see fit.
The dam wasn't begun until after 1975, it was determined after comparisons between aerial photographs. But they've been *ahem* beavering away on the dam for decades. Currently, there are two new dams going up that look like they will eventually be connected to this dam, making a dam almost a full kilometre long. 
Here's a Parks Canada video of the dam from the air:



There's a number of links, so I'll just include a link cluster here.
Parks Canada
Discovery News
EcoInformatics