Yellowstone River: America's Longest Undammed River

The Yellowstone River is the longest undammed river in the contiguous United States, flowing 692 miles from its headwaters in the Absaroka Range of northwestern Wyoming through Yellowstone National Park and across Montana to its confluence with the Missouri River near the North Dakota border.

Introduction

Born in one of the most geothermally active regions on Earth, the Yellowstone descends through the spectacular Grand Canyon of the Yellowstone, crosses the vast agricultural plains of central Montana, and sustains world-renowned trout fisheries along its entire length. Its free-flowing character makes it an increasingly rare treasure among America's major rivers.

Geography & Dimensions

• Length: 692 miles (1,114 km)
• Drainage Basin: 70,000 sq miles
• Average Discharge: 13,000 cu ft/s at mouth
• Source: Absaroka Range, Wyoming (near Younts Peak)

The Yellowstone rises at approximately 12,000 feet elevation in the Absaroka Range south of Yellowstone National Park. It flows north through Yellowstone Lake — the largest high-elevation lake in North America at 7,733 feet — before plunging over the Upper and Lower Falls into the Grand Canyon of the Yellowstone, a dramatic gorge up to 1,200 feet deep painted in yellows and oranges by hydrothermal alteration of volcanic rock.

Below the park, the Yellowstone exits the mountains near Livingston, Montana, and flows northeast across the Great Plains through Billings, Miles City, and Glendive. The river joins the Missouri near the Montana-North Dakota border. Major tributaries include the Bighorn, Tongue, and Powder Rivers, each draining vast stretches of the Northern Plains and the Bighorn Mountains.

Yellowstone National Park

• Grand Canyon of the Yellowstone: Up to 1,200 feet deep, 20 miles long
• Lower Falls: 308 feet — nearly twice the height of Niagara
• Upper Falls: 109 feet
• Yellowstone Lake: 136 sq miles, elevation 7,733 feet

The Yellowstone River's journey through the world's first national park is among the most dramatic stretches of any American river. After leaving Yellowstone Lake, the river drops over the 109-foot Upper Falls and the 308-foot Lower Falls — the largest volume waterfall in the Rocky Mountains. The Lower Falls is nearly twice the height of Niagara Falls and was immortalized in paintings by Thomas Moran that helped convince Congress to create the park in 1872.

The Grand Canyon of the Yellowstone stretches roughly 20 miles below the falls, with walls of rhyolite tuff stained yellow, orange, and red by iron compounds altered by geothermal activity. The canyon gave Yellowstone its name, derived from the Minnetaree word "Mi tsi a-da-zi," meaning "Rock Yellow River." Steam vents and fumaroles along the canyon walls remind visitors of the volcanic forces that shaped the landscape.

Free-Flowing Status & Ecology

• Undammed: Longest undammed river in the contiguous US
• Trout Species: Yellowstone cutthroat, brown, rainbow
• Wildlife: Grizzly bears, bald eagles, ospreys, otters
• Cottonwood Forests: Extensive riparian gallery forests

The Yellowstone is the longest major river in the contiguous United States with no dams on its main stem. Several proposals to dam the river were defeated over the decades, most notably a 1970s proposal at Allenspur near Livingston that was blocked by a coalition of ranchers, anglers, and conservationists. The river's free-flowing character allows natural flooding, sediment transport, and channel migration that sustain exceptional ecological diversity.

The Yellowstone supports world-class trout fisheries, particularly for native Yellowstone cutthroat trout — a subspecies found nowhere else. The river's cottonwood gallery forests provide habitat for bald eagles, great blue herons, and migratory songbirds. Grizzly bears fish the river in Yellowstone Park, and the lower river sustains populations of paddlefish, sauger, and channel catfish.

History & Human Geography

• Indigenous Peoples: Crow (Apsáalooke), Blackfeet, Shoshone
• Lewis & Clark: William Clark descended the Yellowstone in 1806
• Cattle Country: Montana's ranching heartland along the river
• Major Cities: Billings (population 119,000), Livingston, Miles City

The Yellowstone River valley has been home to Indigenous peoples for over 11,000 years. The Crow Nation (Apsáalooke) considered the Yellowstone their homeland, calling it "Elk River." The river provided fish, water, and the rich bottomland that supported bison herds. The Crow, Blackfeet, and Shoshone all used the valley as hunting grounds and travel corridors.

William Clark, traveling separately from Lewis on the return journey in 1806, descended the Yellowstone by canoe from near present-day Livingston to its mouth. Billings, Montana's largest city with a population of about 119,000, grew up along the river as a railroad hub and now serves as the economic center of the northern Great Plains. Ranching remains the dominant land use along the river, with cattle operations dependent on the river for irrigation.

Challenges & Conservation

• 2022 Flood: Historic flooding destroyed homes and infrastructure
• Irrigation Diversions: Significant water withdrawals in summer
• Invasive Species: Lake trout threatening native cutthroat in Yellowstone Lake
• Climate Change: Earlier snowmelt and warmer water temperatures

In June 2022, unprecedented flooding devastated the Yellowstone River corridor, destroying roads, bridges, and homes from Gardiner to Billings. Record rainfall combined with rapid snowmelt sent the river to levels never before recorded at multiple gauging stations. Yellowstone National Park was closed for the first time in its history due to flooding. The event underscored the river's wild power and the vulnerability of development in its floodplain.

Invasive lake trout introduced illegally into Yellowstone Lake in the 1990s have devastated native Yellowstone cutthroat populations, reducing their numbers by over 90 percent. An intensive gill-netting program has removed over 4 million lake trout, but the recovery of cutthroat populations remains uncertain. Climate change is warming water temperatures and shifting snowmelt earlier, stressing trout and altering the river's flow regime.

Key Facts

• The Yellowstone is the longest undammed river in the contiguous US at 692 miles.
• The Lower Falls in Yellowstone Park drops 308 feet — nearly twice the height of Niagara.
• The river supports world-class Yellowstone cutthroat trout fisheries.
• Historic flooding in 2022 closed Yellowstone National Park for the first time ever.
• The river's name comes from the Minnetaree word for "Rock Yellow River."

Fun Facts

• You can wade across the Yellowstone River at its headwaters in the Absaroka Range — a few miles downstream it becomes a raging torrent.
• Yellowstone Lake is so large and so high in elevation that it generates its own weather systems, with sudden storms that can produce 6-foot waves.
• Thomas Moran's paintings of the Grand Canyon of the Yellowstone were so stunning that congressmen reportedly pulled out their wallets to fund the national park on the spot.
• The Yellowstone is one of the few rivers in the lower 48 where you can catch a native trout species on a fly rod in completely wild, undammed water.

Final Thoughts

The Yellowstone River is a living symbol of wild America — a major river that still flows freely from mountain to plain, sustaining world-class fisheries, diverse wildlife, and a way of life rooted in the Northern Rockies and Great Plains. Protecting its free-flowing character is one of the great conservation achievements of the American West.