Which river is the longest in both Alaska and Canada's Yukon territory?

The Yukon River is the longest river in both Alaska and Canada’s Yukon territory. Its 3,190-kilometre course begins in northwestern Canada and ends in Alaska’s Yukon–Kuskokwim Delta.

The river’s generally accepted source is the Llewellyn Glacier at the southern end of Atlin Lake in British Columbia. It then passes through Yukon, including Whitehorse, Carmacks and Dawson City, before crossing Alaska and reaching the Bering Sea. Its upper course was once called the Lewes River.

The Yukon was a crucial transportation route during the Klondike Gold Rush of 1896–1903, when paddle-wheel steamboats moved people and supplies through the region. The name also gave Canada’s Yukon territory its modern designation. Porcupine and Tanana are important tributaries, not the main river, while the Kuskokwim is another major Alaskan river system. The Yukon’s enormous basin also supports one of North America’s great salmon fisheries.