The Stewart River is a 533-kilometre (331 mi) tributary of Yukon River in the Yukon Territory of Canada. It originates in the Selwyn Mountains, which stand on the border between the Northwest Territories and the Yukon Territory. From there, the Stewart flows west, past the village of Mayo. The river is crossed by the Klondike Highway at the village of Stewart Crossing, and the highway parallels the river westward for about 56 kilometres (35 mi). After leaving the highway, the river travels southwest until it intersects the Yukon River 112 kilometres (70 mi) south of Dawson City. The mostly abandoned village of Stewart River is located at the mouth of the river.

The Yukon River is a major watercourse of northwestern North America. From its source in British Columbia, it flows through Canada's territory of Yukon. The lower half of the river continues westward through the U.S. state of Alaska. The river is 3,190 kilometres (1,980 mi) long and empties into the Bering Sea at the Yukon–Kuskokwim Delta. The average flow is 6,400–7,000 m3/s (230,000–250,000 cu ft/s). The total drainage area is 833,000 km2 (321,500 sq mi), of which 323,800 km2 (125,000 sq mi) lies in Canada. The total area is more than 25% larger than Texas or Alberta.