Geography of Montana Rivers
Running north and south, through Montana’s western terrain, is the Continental Divide of the Rocky Mountains, separating Montana into two drainages, one west-sloping and the other east-sloping.
Consequently, rivers flowing west off the divide flow by way of the Columbia River system, delivering their water to the Pacific Ocean. Rivers flowing east off the divide, flow via the Missouri River system, moving toward the Atlantic, specifically the Gulf of Mexico.
Interestingly, a third drainage, near the Montana-Canadian border, moves water north from Montana’s Glacier National Park, north to Canada’s Hudson Bay and then east to the North Atlantic Ocean.
Montana Rivers on the Eastern Slope of the Continental Divide
Out of Montana flow waters that form some of North America’s great waterways–the Missouri and the Yellowstone Rivers–and many world-class fly fishing streams.
Three Forks, Montana is home to the “Wide Missouri,” the longest river–2341 miles–in North America.
On the east side of the Northern Rocky Mountain Continental Divide, the Montana land sends more than 50% of its runoff north by way of the great Missouri River, formed by the confluence, just north of Three Forks, MT, of the Madison River, Jefferson River, and Gallatin River.
The Gallatin River
West Gallatin River: Born from within the bounds of Yellowstone National Park, the West Gallatin River flows north through the Gallatin Canyon toward Three Forks, Montana and is about 90 miles long with a drainage area of from 20 to 30 miles wide.
East Gallatin River: Its sister, the East Gallatin River is created by the streams flowing forth from slopes east of the Gallatin Canyon. The West Gallatin River and the East Gallatin River meet to form the Gallatin River north of Manhattan, Montana.
The Jefferson River
The child of both the Beaverhead River and the Big Hole River, the Jefferson River first appears in the town of Twin Bridges, Montana, from which it flows northeast, meeting the Madison River north of Three Forks, Montana, from which the two then flow about two miles farther north to combine with the Gallatin and Madison rivers to form the Missouri River.
The Madison River
Famous for its world-class trout fishing, the Madison River also arises from within Yellowstone National Park where the Gibbon River and Firehole River meet. The Upper Madison, as it is called at this point, then flows north some 20 miles to man-made Hebgen Lake, then on to nature-made Quake Lake, then 50 miles to man-made Ennis Lake, in Ennis, Montana, after which it flows 40 miles as the Lower Madison River to Three Forks, Montana, after cutting through Bear Trap Canyon and the flat terrain south of Three Forks, MT.
For eons the Missouri River has flown northward from Three Forks, Montana at 4130 feet above sea level, cutting deep canyons through the Big Belt Mountains as it makes its way toward the mighty Mississippi River. When it reaches the Plains, the Missouri flows through the northeastern portion of Montana at much lower elevations than at its starting point in Three Forks, MT and travels 1029 miles, creating Montana’s longest river.
The Yellowstone River, flowing through Livingston, Montana, the Missouri River’s principal tributary in Montana, flows from Yellowstone Lake in Yellowstone National Park, Wyoming, and through its channel, the Yellowstone courses water from the southeastern section of Montana to the Missouri River, a bit east of the Montana and North Dakota state line. The Yellowstone River is one of the longest un-dammed rivers remaining in the world and rivals the Missouri in the waters it handles from Montana.
The Roe River is considered to be the world’s shortest river at 201 feet in length. Running from Giant Springs, Montana to the Missouri River in Great Falls, MT, the Roe River discharges 156 million gallons per day into the Missouri River.