What is Canada's largest river system?

Canada’s largest river system is the Mackenzie River system.

The system combines the Mackenzie, Slave, Peace, and Finlay rivers. Its ultimate headwater is near Thutade Lake in British Columbia, while the Mackenzie’s main stem begins at Great Slave Lake in the Northwest Territories and flows north to the Beaufort Sea.

Including its major tributaries, the system is about 4,241 kilometres long. Its drainage basin covers roughly 1.8 million square kilometres—nearly one-fifth of Canada—and reaches into British Columbia, Alberta, Saskatchewan, Yukon, and the Northwest Territories.

A common mix-up is confusing the Mackenzie system with the St. Lawrence system, which has greater discharge in Canada. The Mackenzie is the country’s longest river system and one of the world’s major Arctic-draining river networks.