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.
List of longest rivers of Canada
Sources report hydrological quantities with varied precision. Biologist and author Ruth Patrick, describing a table of high-discharge rivers, wrote that data on discharge, drainage area, and length varied widely among authors whose works she consulted. "It seems," she said, "that the wisest course is to regard data tables such as the present one as showing the general ranks of rivers, and not to place too much importance on minor (10–20%) differences in figures."