Whomever came up with that phrase clearly had these critters in mind:
A Canadian ecologist has discovered the world’s largest beaver dam in a remote area of northern Alberta [….] researcher Jean Thie said Wednesday he used satellite imagery and Google Earth software to locate the dam, which is about 850 metres (2,800 feet) long on the southern edge of Wood Buffalo National Park.
Construction of the dam likely started in the mid-1970s, said Thie, who made his discovery quite by accident while tracking melting permafrost in Canada’s far north. “Several generations of beavers worked on it and it’s still growing,” he told AFP in Ottawa.
Just to give you a little idea of how large this dam actually is, the The Hoover Dam is only 379 meters wide.