The Kootenay (Kootenai in the U.S. and historically called the Flatbow) 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 781 kilometres (485 mi) 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.