Water is a defining, dynamic, and driving force in the Greater Yellowstone Ecosystem. The ecosystem’s wild rivers are so significant to its identity that Greater Yellowstone is often called “the headwaters of the West.” When I first heard this phrase, I remember trying to absorb the significance of such a title – it reinforced for me that this place is special, but what does it really mean to be “the headwaters of the West?” 

The Journey 

It’s early July in the Tobacco Root Mountains of southwest Montana. The last evidence of winter remains frozen in the shadows of 10,000-foot peaks, piles of snow on the ridgeline disappearing slowly into trickles of ice-cold water. As a trickle carves a path downhill, it intermingles with other small trickles descending all around the rocky bowl. By the time the trickle reaches the basin floor, it’s a few inches wide and identifiable by its quiet babble. Less than a mile later, it’s a small, foot-and-a-half-wide stream — a collection of snowmelt from surrounding hillsides and ridges.  

Soon after, it’s significant enough to have a name – Mill Creek. Miles later, joined by other streams of meltwater, Mill Creek finally reaches the bottom of the canyon, where it flows across the Ruby Valley and joins the Ruby River.  

The Ruby River meanders northeast through ranching communities to its confluence with the Beaverhead and Big Hole rivers, which in turn form the Jefferson River, which further east helps form the Missouri River. While you might not have heard of the Ruby or Jefferson rivers, you may know the Missouri River. The Missouri River is the longest river in the United States and a major tributary of the Mississippi River. 

Across Greater Yellowstone, rain and snowmelt form streams and rivers that follow paths like this one. By tracing the journey of a drop of water from its existence as snowmelt high in the mountains of southwest Montana, across thousands of miles and 13 states, before ending up in the Gulf of Mexico, we can start to understand how watersheds work, and how interconnected our world truly is. Within the Greater Yellowstone Ecosystem, we find the headwaters of four major river systems, collectively responsible for providing clean water to upwards of 65 million people across the United States. 

The Lifeblood of a Landscape 

Rivers are the lifeblood of the American West. Clean water is essential to the health and survival of our natural ecosystems and human communities; across the western United States, rivers and streams supply our drinking water, support myriad industries, and sustain wildlife and wild lands. As important as they are, rivers are also complex, and the language and terminology to describe them equally complicated. To understand rivers, and to start to understand the phrase “the headwaters of the West,” we must begin with a few key terms. 

Rivers are often discussed in the context of their watershed. A watershed is simply the name for an area of land within which all rainfall, snowmelt, rivers, and streams drain to one specific point – typically a specific waterbody. No matter where you are in the world, if you are on land, you are in a watershed.  

Closely related to a watershed is the term “river basin.” A river basin is an area of land comprised of many different watersheds that contribute to a given river. For example, the Missouri River Basin is the cumulative area of all the watersheds of smaller waterways that flow into the Missouri River. Another accompanying term is “river system.” A river system is a river and all of its tributaries. 

Watersheds vary widely in size. A small creek may have a watershed that’s one hundred square meters, while the Yellowstone River Watershed drains close to 40,000 square miles of land. Not all water in a watershed travels over land – water can seep into the soil and become groundwater. 

Another term we use often when discussing rivers and river systems is “headwaters.” The headwaters of a river are the streams that form the very beginning of a river, often too small to have a name. Remember the trickles of snowmelt high in the Tobacco Root Mountains that eventually formed the Ruby River? This snowmelt was the headwaters of the Ruby and subsequently the Missouri and Mississippi.  

Among the more well-known and beloved of the GYE’s rivers are the Green River, Snake River, and Missouri River. These rivers are major tributaries of the Colorado River, Columbia River, and Mississippi River respectively. The Bear River, the largest tributary by volume to the Great Salt Lake, is another significant river with headwaters in Greater Yellowstone. These four rivers, four of the West’s most significant river systems, can all be traced back to headwaters in the mountains of the Greater Yellowstone Ecosystem.  

The Green-Colorado River System 

The Green-Colorado River System has headwaters in the Bridger-Teton National Forest of western Wyoming. Originating from snowmelt and glacial melt high in the Wind River Range and Wyoming Range, the Green River flows south, creating a lush riparian corridor through desert and sagebrush steppe for just over 700 miles before its confluence with the Colorado River in Utah. The Green River is the largest tributary by volume to the Colorado River.  

The Colorado River continues its journey southwest through Arizona, Nevada, California, Baja California, and Sonora before its terminus in the Gulf of California. Along its journey it carves the Grand Canyon, provides freshwater for over 40 million people, and sustains multi-billion and trillion-dollar industries.  

Snake-Columbia River System 

The Snake River originates in two of the nation’s most renowned national parks: Yellowstone and Grand Teton. From snowpack and springs in the parks and surrounding mountain ranges, the Snake River is born in Wyoming and flows just east of and parallel to the Teton Range before arcing into Idaho. The Snake meanders west across Idaho, supplying irrigation for potatoes, sugar beets, alfalfa, and other crops, as well as drinking water for cities along the way, before heading north into Washington. The Snake is also a world-class salmon, steelhead, and trout fishery. 

In Washington, the Snake River reaches its confluence with the Columbia River after a 1,000-mile journey. For the last 300 miles of its journey, the Columbia forms the border between Oregon and Washington before spilling into the ocean just north of Portland. Collectively, the rivers of the Columbia River System drain more water to the Pacific Ocean than any other river system in North or South America. Over eight million people rely on the Snake-Columbia River System to meet industrial, agricultural, municipal, and recreational needs. 

Missouri-Mississippi River System 

The Mississippi River Basin is the largest river basin in the United States, draining about 40 percent of the Lower 48. While not all water in the Mississippi River originates in the Greater Yellowstone Ecosystem, the Mississippi’s largest tributary – the Missouri River – does. The Missouri is formed in southwest Montana by the confluence of three rivers, and is later joined by the Yellowstone River. These rivers have their headwaters in the mountains of Yellowstone National Park, southwest Montana, and Wyoming’s Wind River Range. Before they even come together to form the Missouri, they have supplied water to countless agricultural operations, sustained world-class trout fisheries, and provided ample recreation opportunities. 

The Missouri joins the Mississippi River in St. Louis, and the Mississippi subsequently supplies drinking water for more than 18 million people in 50 cities including St. Louis, Memphis, and New Orleans, and supports agriculture, shipping, industry, and recreation across much of the United States. 

Bear River & the Great Salt Lake 

At the southern extent of the Greater Yellowstone Ecosystem in the Wyoming Range and southeastern Idaho is the headwaters of the Bear River. Along its horseshoe-shaped journey through Utah, Wyoming, Idaho, and back through Utah, the Bear largely supports agriculture, along with industry, municipalities, energy generation, and recreation. The 500-mile Bear River is the longest river in the United States that does not empty into an ocean; instead, it supplies about 60 percent of the inflow to the Great Salt Lake. 

The Bear River, its tributaries, and the Great Salt Lake itself support a host of human and ecological communities. Its headwater streams provide critical native fish habitat, and the Great Salt Lake supports eight to ten million birds along their migratory paths. 

The scale, scope, and significance of these systems that begin in Greater Yellowstone are difficult to comprehend. These four river systems collectively serve upwards of 65 million people across the nation and water originating in Greater Yellowstone streams passes through and supports 21 states – 17 of which are west of the Mississippi and comprise 75 percent of all states west of the Mississippi River. Alongside these human communities exist dynamic ecosystems with intricate webs of mammal, plant, fish, and bird life that too depend on the clean, cold water that originates in Greater Yellowstone. Piecing together these four immense river basins with headwaters in Greater Yellowstone, a vision of “the headwaters of the West” and its significance takes shape. 

The Foundation of Healthy Ecosystems 

“A river system is only as resilient as its headwater streams,” Greater Yellowstone Coalition’s Western Wyoming Conservation Associate Teddy Collins explains. Teddy has spent countless hours inventorying headwater streams in Wyoming’s Bridger-Teton National Forest to evaluate their characteristics in the context of potential protections under the Wild & Scenic Rivers Act – an act that ensures streams with outstanding natural, cultural, and recreational values remain free-flowing. With so many millions of people and ecological communities here in Greater Yellowstone and downstream relying on the clean water that originates here, protecting these waterways now and for future generations is essential.  

“The areas of highest biodiversity are riparian habitats and river ecosystems,” Teddy shares. “Without these waterways, we don’t have the amazing flora and fauna and species diversity that we see in Greater Yellowstone... without these headwater streams or riparian habitats, and the integrity of those habitats, you lose the integrity of the ecosystem.” 

Not only are headwater streams important for healthy rivers downstream, but they are also essential to the lands and wildlife with which they are inextricably intertwined. There are countless species sustained by headwater streams including the grizzly bear, which heavily utilizes riparian corridors, and a number of increasingly scarce native fish. 

Sierra Harris, GYC’s climate change coordinator who has spent almost two decades working to protect headwater streams and river systems in southwest Montana, explains that “these headwater streams, fed by snowmelt, stay cold and provide critical habitat for fish species. If you think about the arctic grayling or westslope cutthroat trout, we could have these species literally blink out at any time – and they don’t live in the Yellowstone River or the Missouri or other big rivers. They live in the headwater streams.” And with the ever-pressing issue of climate change, Sierra notes that “as temperatures rise in rivers in the face of climate change, fish need to find refuge in cold clean water that headwaters provide.”  

What We Do Here Matters 

As the birthplace of four major river systems that span much of the western United States, the Greater Yellowstone Ecosystem is “the headwaters of the West.” This means that how we manage and protect our waters here at the very beginning of the system has implications for much of the western United States and all those from the Pacific Ocean to the Gulf of Mexico that live downstream. What we do here matters. 

Kurt Imhoff, GYC's senior climate conservation associate, has spent his career working to protect river and riparian habitats across the West. He emphasizes that protecting headwater streams is an exercise in watershed-scale stewardship. “We're not just safeguarding aquatic ecosystems and water supply for those living here. These benefits trickle downstream – working in a headwaters system really has an outsized impact." 

The importance of headwater streams and Greater Yellowstone’s place as the headwaters of the West cannot be understated. Sierra puts it plainly: “Every drop of water that is protected in the headwaters benefits all downstream water users. There are no upper headwaters of the headwaters, it starts here. We have a big responsibility to be good stewards and that’s no small task.” 

Protecting Rivers Starts with All of Us 

Protecting headwaters and safeguarding cold, clean water for millions of people and the wildlife and ecosystems we know and love starts with all of us. Whether you live in the Greater Yellowstone Ecosystem or dream about floating, fishing, or admiring its rivers from afar, you can help protect these waterways now and for future generations.  

No matter where you live, you are living in a watershed – protecting America’s river systems can start in all of our backyards. You can make a difference by getting involved with your local watershed group, voting on water issues, speaking up for waterways, volunteering for river clean ups, watering your lawn less, or using less fertilizer to reduce pollutants entering waterways. 

To stay up to date with our work to protect the streams and rivers of Greater Yellowstone, or to be notified when we need your voice to advocate for these significant waterways, sign up to receive our emails.  

The waters of the Greater Yellowstone Ecosystem are remarkable, and it’s our job to keep them that way. Protecting the headwaters of the West is essential for not just those of us that live here, but all those that live downstream. 

—London Bernier, Communications Associate

Glossary of Terms: 

• Confluence – when two or more flowing waterbodies join to form one. 

• Headwaters – the streams that form the very beginning of a river. 

• Riparian corridor – the habitat along the edges of rivers and streams. 

• River basin – an area of land comprised of many different watersheds that contribute to a given river. 

• River system – a river and all of its tributaries. 

• Tributary – a river or stream flowing into a larger river, stream, lake, or waterbody. 

• Watershed – an area of land within which all rainfall, snowmelt, rivers, and streams drain to one specific point – typically a specific waterbody.