Which is the longest river in Canada?

The Mackenzie River is the longest river in Canada. It runs for about 4,240 kilometres from Great Slave Lake in the Northwest Territories to the Beaufort Sea, an arm of the Arctic Ocean.

The river flows entirely within Canada, although its wider river system includes major tributaries such as the Peace and Athabasca rivers. Those tributaries extend the drainage network across parts of Alberta, British Columbia, Saskatchewan, and the Northwest Territories. The Mackenzie basin covers a vast region of boreal forest, wetlands, lakes, and tundra.

A common mix-up involves the Yukon and St. Lawrence rivers. Both are associated with Canada and are very long, but the Yukon continues through Alaska, while the St. Lawrence forms an international waterway and includes the Great Lakes system. Depending on whether a quiz counts only the main channel, the entire drainage system, or rivers crossing national borders, rankings can differ; for the standard Canada-only answer, Mackenzie is the accepted choice.