clock menu more-arrow no yes mobile
Millie von Platen for Vox

Filed under:

These 8 species depend on the Colorado River. What happens as it dries up?

Wildlife needs water, too.

Benji Jones is a senior environmental reporter at Vox, covering biodiversity loss and climate change. Before joining Vox, he was a senior energy reporter at Insider. Benji previously worked as a wildlife researcher.

Part of the issue The 100-year-old-mistake that’s reshaping the American West from The Highlight, Vox’s home for ambitious stories that explain our world.

Wedged between two vast stretches of farmland in Southern California, the Salton Sea doesn’t seem habitable. It smells foul, like rotting eggs. The shore is crusted with salt and littered with tires and old glass bottles. And the only water flowing into it is runoff from farmland. The Salton Sea is literally fed by wastewater.

Yet here in the desert, the sea is a haven for birds. Roughly 270 avian species regularly use the lake — the largest in the state — including white and brown pelicans, double-crested cormorants, and snowy plovers. In past decades, for example, winter would draw millions of eared grebes, migratory waterbirds with piercing red eyes and golden feathers that fan out from their cheeks. The lake is something of a birder’s paradise.

But like many of the United States’s important wildlife habitats, the Salton Sea is shrinking. Evaporation is outpacing the inflows of water running off from farms, causing the lake to recede and turning it incredibly salty. There’s so much salt now that few fish and other aquatic critters can survive, which means fish-eating birds like pelicans are vanishing, according to Robert McKernan, a retired ornithologist who’s been studying the sea since the ’70s.

The decline of the Salton Sea is tied to another dwindling water body, some 60 miles east: the Colorado River. A century of mismanagement, coupled with two decades of drought that’s been deepened by climate change, has drained the river to record lows. The river’s many users — including golf courses, households, the city of Phoenix, Arizona, and farmers in the nearby Imperial Valley and Coachella Valley — have had to cut back their water use as a result. It’s runoff from these farms that feeds the Salton Sea.

Over the last two decades, farmers here have slashed their usage substantially, causing the sea to drop. And now, they’re likely to cut back even more, further threatening the important ecosystem. It’s a complex problem: On the one hand, it’s good that growers have become more efficient with a limited resource, but it’s come, to an extent, at the expense of an important habitat for birds.

The ongoing changes to the Salton Sea are just one example of how the Colorado River crisis affects not only human lives, but the lives of wild organisms — the fish, birds, mammals, and plants that have lived in the river basin for thousands of years. Humans depend on this diversity of life. Healthy river ecosystems help keep the river clean; they limit the destruction of wildfires and pests; and they provide a sustainable source of food for the basin’s inhabitants.

Since the 1900s, the greatest threats to wildlife in the basin, which spreads across seven Western states, have been dams and other structures that control the river, utterly transforming how it operates. But the recent water shortage, along with drought and rising temperatures, is further changing ecosystems along the river.

This story is about those changes. Through the lens of seven animals and one plant, we explain how a declining Colorado River is influencing the natural world. It’s not all bad: Nature has a propensity for adaptation, and humans are helping restore some of its most important habitats, including parts of the Salton Sea. What is worrying is that climate change is set to make many of the existing problems worse.

Millie von Platen for Vox

Cutthroat trout

The Colorado River begins in the Rocky Mountains of Colorado, where it pours out of a snow-fed lake and runs south through marshy meadows and beaver ponds. The headwaters of the Colorado River, and other coldwater streams that feed into it, are home to a number of fish, including Colorado River cutthroat trout. A native fish with olive-colored scales and black polkadots, cutthroat trout have signature red markings behind their gills (hence their somewhat gruesome name).

Competition with nonnative fish, such as brown trout, along with drought and rising temperatures, are imperiling the species, which is now found in roughly 10 percent of its native range in the Colorado River basin. These fish need cold, oxygen-rich water, but as streams shrivel during drought, they heat up and hold less dissolved oxygen — making the water much less hospitable.

Millie von Platen for Vox

Bark beetles

The bark beetle is a small insect found throughout the Rocky Mountains, in the Colorado River basin and beyond. Although they’re no larger than a grain of rice, these native beetles are incredibly destructive. They bore into trees, disrupting the flow of nutrients into the plants. Along with symbiotic fungi that bark beetles are known to team up with, this process can weaken or kill the trees.

In the past three decades, bark beetles (of a number of different species) have killed more trees than all wildfires in the Western US. Climate change and drought only makes the threat of bark beetles more severe. Rising temperatures can cause their numbers to balloon. And when there’s less water available, trees have a much harder time fighting off a bark beetle attack.

Millie von Platen for Vox


If bark beetles are unwanted pests in the upper Colorado River, beavers are ones we want. By the early 1900s, trappers had nearly wiped them out from North America, and today, people still kill these large rodents because they hack down trees and block streams. While beavers are still perceived in some places as pests, their reputation has been improving.

Many water experts now see beavers as a potential antidote to drought and the problems it’s causing along the Colorado River. The snowpack in some mountain regions is now melting earlier, meaning there’s less water flowing downstream later in the year. By damming waterways, beavers help slow down the flow of water, keeping the landscape wet for longer. They also create cold ponds that benefit fish like cutthroat trout, and keep trees hydrated so they’re less likely to burn in a wildfire or fall victim to bark beetles.

Millie von Platen for Vox

Smallmouth bass

From the Rocky Mountains, the river wanders west into Utah, passing through Canyonlands National Park, before running into the Glen Canyon Dam, where it forms Lake Powell. In the ’80s, wildlife officials introduced the smallmouth bass, a nonnative species, into the lake for sport fishing. It was good for tourism, perhaps, but bad for the local ecology: Smallies, as they’re sometimes called, like to eat rare native fish — like the highly threatened humpback chub. The chub, a strange-looking fish with a fleshy lump behind its head, has been recovering downstream in the Grand Canyon, partly because they’re guarded against smallmouth bass by Glen Canyon Dam. Smallies like warm water, and the intake for the dam is deeper down where it’s cold.

At least, that’s how it used to be. Overconsumption of the river, mixed with drought, has caused the water level in Lake Powell to recede. And now, the intake valve is near the warm waters of the lake’s surface, allowing the invasive fish to pass through. Scientists recently found smallies below the Glen Canyon Dam, which could further imperil the humpback chub and the entire native ecosystem of the iconic national park.

Millie von Platen for Vox

Razorback sucker

As the Colorado River continues south past the Grand Canyon, it bends around Las Vegas and runs into the Hoover Dam, before reaching a reservoir called Lake Mohave. The lake, tucked into the southern tip of Nevada, harbors one of the basin’s remaining population of razorback suckers. An endangered fish with green scales, a yellow belly, and a big mass behind its head, the sucker was once abundant in warm waters of the Colorado River and its tributaries.

Now they’re incredibly rare, persisting in only a small sliver of their native range. In Lake Mohave, suckers have declined from roughly 60,000 individuals in the ’80s to just a few thousand in recent years — most, if not all, of which were reared in captivity and reintroduced by wildlife officials. Suckers face pretty much every threat there is along the river, from invasive species that prey on their eggs and babies, to giant infrastructure projects that have dramatically altered the river’s flow. Their decline, buffered to an extent by captive rearing and restocking programs, is emblematic of the broader ways the river has been changing.

Millie von Platen for Vox

American white pelican

Just north of Yuma, Arizona, the Colorado River runs into the Imperial Dam. The dam diverts part of the river into the All-American Canal, which carries water more than 80 miles west to farmland in California’s Imperial Valley. It’s runoff from those farms that sustains the Salton Sea. Roughly 20 years ago, when farmers started using less water (as part of an agreement between the Imperial Valley and the city of San Diego, to send more water to urban users, which I explain here) the Salton Sea began shrinking.

With less fresh water flowing in, the large, shallow lake began evaporating and becoming too salty for fish, causing declines in fish-eating birds. Thousands of American white pelicans, for example, used to visit the sea at one time, McKernan, the ornithologist, said. Now, he said, you can only see a few hundred. “There’s just not enough fish for them to eat anymore,” said Andrea Jones, director of bird conservation at Audubon California. Should farming districts that feed the Salton Sea face additional cutbacks — which experts anticipate — the lake could become less hospitable to many birds. That’s troubling considering that California has already lost more than 90 percent of its wetlands. The Salton Sea is one of its last remaining habitats.

Millie von Platen for Vox

Yuma Ridgway’s rail

If you follow the river further south, past Yuma and into northwest Mexico, you’ll reach the delta, the river’s end. The delta has been mostly dry for decades now — all the water is sucked out further upstream — but there are some habitats that remain wet, thanks again to runoff from farmland. Salty water pouring off of fields near Yuma trickles into Mexico, where it flows into a 40,000-acre wetland called Ciénega de Santa Clara. It’s an important habitat for birds, and especially for the Yuma Ridgway’s rail, a brown, crustacean-loving species with a long and narrow beak.

As much as three-quarters of the world’s Yuma Ridgway’s rail population lives in this wetland, according to Jennifer Pitt, the National Audubon Society’s Colorado River program director. This habitat, too, could be threatened if farmers in southwestern Arizona start using less water on their crops, or reroute the runoff into a desalinization plant so it can be reused on farmland in Mexico. Ironically, while agriculture is a major driver of wildlife declines worldwide, many farms fed by the Colorado River help sustain birds.

Millie von Platen for Vox

Cottonwood tree

The most iconic organism along the Colorado River is arguably not an animal but a woody plant: the cottonwood. This tall, deciduous tree grows along the edge of rivers throughout much of the basin and in the delta, providing habitat and food for a wide range of animals and helping stabilize the riverbank. “It’s a keystone species,” said Karl Flessa, a professor of geosciences at the University of Arizona, referring to organisms that help hold ecosystems together. (There are a few different cottonwood species in the Colorado River Basin.)

Cottonwoods are still abundant in the West, yet they rely on two things that are increasingly limited: water and spring floods, which scour the ground and give seedlings a space to take root, Flessa said. They also face competition with a nonnative tree, the saltcedar, that can survive more easily without a recurring surge of fresh water. What happens to cottonwoods without water is apparent in the dry delta, where many cottonwood trees have disappeared.

Over the last decade, however, environmental groups have restored parts of the delta, planting groves of cottonwood and willow trees, and finding ways to bring in water. Those efforts are encouraging the return of wildlife — the Yuma Ridgway’s rails, beavers, and other species that have lived here for thousands of years.

Future Perfect

How the US is preparing to fight — and win — a war in space

Even Better

How to make your anger work for you

Future Perfect

We have treatments for opioid addiction that work. So why is the problem getting worse?

View all stories in The Highlight

Sign up for the newsletter Today, Explained

Understand the world with a daily explainer plus the most compelling stories of the day.