Mackenzie River
At , the Mackenzie River drainage basin encompasses nearly 20 percent of Canada. About , or 54 percent of the basin, lies above Great Slave Lake. Permafrost underlies about three-quarters of the watershed, reaching up to deep in the Mackenzie Delta. As a whole, the Mackenzie basin receives only meager to moderate rainfall, averaging over the entire basin, though mountain areas experience much higher precipitation, and areas near and north of the Arctic Circle receive much lower precipitation.
Western Canada
The Canadian Rockies are part of a major continental divide that extends north and south through western North America and western South America. The continental divide also defines much of the border between Alberta and British Columbia. The Columbia and the Fraser Rivers have their headwaters in the Canadian Rockies and are the second- and third-largest rivers, respectively, to drain to the west coast of North America. To the west of their headwaters, across the Rocky Mountain Trench, is a second belt of mountains, the Columbia Mountains, comprising the Selkirk, Purcell, Monashee and Cariboo Mountains sub-ranges.