High Quality Content by WIKIPEDIA articles! The Kootenay (Kootenai in the U.S. and historically called the Flatbow) is a major river in southeastern British Columbia, Canada and the northern part 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 origins in the Kootenay Ranges of the Canadian Rockies, exiting British Columbia`s East Kootenay region via northwestern Montana and the northernmost Idaho Panhandle to return to Canada in the West Kootenay region, where it ends at the city of Castlegar, British Columbia.