What is the longest river in Canada that flows out of Great Slave Lake?

The Mackenzie River is the longest river in Canada and flows out of Great Slave Lake. Spanning approximately 1,738 kilometers (1,080 miles), it travels northwest through the Canadian Northwest Territories before emptying into the Arctic Ocean. The Mackenzie is a critical component of the hydrological system in northern Canada and is known for its remarkable size and significance in the region's ecology and economy.

In contrast, the Columbia River originates in the Rocky Mountains of British Columbia and primarily flows into the United States, while the Red River flows through the United States and Canada, originating in Minnesota and eventually joining the Assiniboine River. The Mississippi River, one of the longest rivers in North America, flows entirely within the United States, making it unrelated to Canada’s river systems. Thus, the Mackenzie stands out as the correct choice due to its direct connection to Great Slave Lake and its status as the longest river in that region.