The Kootenay is a major river in southeastern British Columbia, Canada and northern parts of the U.S. states of Montana and Idaho. It is one of the uppermost major tributaries of the Columbia River, which is the largest North American river that empties into the Pacific Ocean. The Kootenay River runs 781km from its headwaters in the Kootenay Ranges of the Canadian Rockies, flowing from British Columbia's East Kootenay region into northwestern Montana, thence into northernmost Idaho Panhandle and returning to British Columbia in the West Kootenay region, where it joins the Columbia at Castlegar.Born in glaciers and flowing through a rugged landscape of mountains and valleys, the river drains an isolated and sparsely populated region of the Pacific Northwest. From its highest headwaters to its confluence with the Columbia River, the Kootenay falls more than two kilometers in elevation. Although comparable in length, watershed and discharge to the Columbia above the confluence, the Kootenay is of a notably different character; its much steeper gradient results in the formation of many rapids.