It’s not exactly news that the rivers of the western U.S. are in trouble.

For decades, their water has been siphoned off by climate change-fueled heat and an ever-growing human demand for grassy front lawns and long showers. The biggest user of river water by far, though, is agriculture—and new research shows that across the western United States, a third of all consumed water goes to irrigate crops not for human consumption, but that are used to feed beef and dairy cattle. In the Colorado River basin, it’s over 50 percent.

The burgers, steaks, yogurt, and ice cream Americans eat in abundance, the new results show, is directly related to the overuse of river water—leaving the ecosystems and communities that depend on those rivers drastically stressed under even the best of circumstances. During bad drought years, the stress ratchets up on many western rivers, nudging over 50 species of fish closer to extinction or imperilment, estimates the study, published this week in Nature Sustainability.

The good news, says Brian Richter, the lead author of the study and a water expert at Sustainable Waters, is that the detailed tracing they’ve done gives growers, policymakers, and consumers a lot of power to make different choices.

“We could see the water being pulled out of a specific river, going to a specific feedlot or dairy, and then as a product going to a specific place where it was consumed,” he says. And that kind of detail can be leveraged to make very targeted changes that could save vast amounts of water.

Waving fields of green

The realization crystallized as Richter was driving around the western states on a road trip, towing a trailer and crisscrossing mountains, high deserts, and forests. The flat stretches of desert were landscapes he’d known since childhood: sprays of sage scrub dotting subtle, dry vistas. But the valleys he’d pass through were lush and green, blanketed with verdant vegetation. Alfalfa. Hay. Sorghum. Acres of it, waving in the dry air, destined not for people’s plates but for cows. In turn, those cattle would be turned into steaks or burgers eaten by people tens or hundreds or thousands of miles away.

The fields could only grow, Richter knew, because of vast infusions of irrigation water. He wondered: Could he and colleagues figure out exactly where the water that fed the alfalfa that nourished the cows that ended up on the plates of consumers in far-flung cities came from?

It turned out they could.

They tracked the water taken out of rivers and streams in each little fraction of a watershed to the places it was being used to irrigate crops, and in many cases could trace its journey to farms or counties that grew certain cattle feed crops. Then, they could use economic data about supply chains to trace the journey of those crops from farm to feedlot, and from feedlot to the place the beef or dairy products were ultimately sold.

They could also estimate how much the water withdrawals from individual watersheds would endanger fish populations living in those delicate waters. Low summer water flows in rivers across the region, particularly when caused by water extractions that end up irrigating cattle feed crops, have added to the local extinction risk faced by nearly 700 species of fish.

“The summer—that’s the growth season for many species of fish, when the water is needed the most,” says Marguerite Xenopoulos, an aquatic ecologist at Trent University in Ontario. “When water is taken out of the river, and it’s tied to some aspects of species life cycles of the fish, they can be particularly hard hit.”

Where’s the beef?

Overall, the beef grown with crucial river water supplies was eventually routed mostly to major urban areas in the West: Los Angeles and Long Beach and the Bay Area of California; Portland, Oregon; Denver, Colorado; and Seattle, Washington. If they broke it down per capita, Oregon, Idaho, and some hotspots in Texas ate the most beef associated with river water depletion.

It’s not particularly surprising that the water diverted from fish living in streams in the high deserts ends up as a bite of a burger eaten in Laredo, Texas, says Megan Konar, an environmental engineer at the University of Illinois at Urbana-Champaign who has worked on similar supply chain analyses.

That’s how supply chains work: resources from one place feed demand in faraway spots, and cities—jammed full of people who all need to eat, drink, wear clothes, and more—use up a lot of those resources “virtually,” because of tethers in the complicated, globe-spanning modern supply chain.

So on one hand, a burger-eater in Texas or Idaho or New York can lighten their water load on water-stressed parts of the land if they choose to eat something besides beef. But ultimately, the solutions to the western water crisis require a bigger, more comprehensive approach.

“This is a collective action problem; we can’t leave it up to individual consumers to solve it,” says Konar.

It’s not just beef that’s drying up the rivers

Some 23 million acres of alfalfa are grown across the U.S. The plant was ferried west during the Gold Rush of the 1850s, when it was a crucial feed source for the cows, horses, and other grazing animals that settlers relied on for food and labor. Beef cattle and dairy industries expanded across the western U.S. over subsequent decades, but the animals needed more feed than they could forage from the dry landscapes—so feed crops like alfalfa became more and more critical to the burgeoning herds. As large-scale irrigation projects bloomed across the west, more and more cattle-feed crops could be grown, supporting ever-expanding herds.

“It’s an amazingly adaptable crop,” says Brad Udall, a climate and water expert at Colorado State University. “It’ll grow from hottest desert to highest mountain, and get you multiple cuttings a year, and it’s pretty easy to grow.”

Well over a century of land-use history, policy decisions, and complicated water rights fights have led to the system in place today. But there’s an extra threat layered on top of the history now: climate change.

In the Colorado River, which supplies water to over 40 million people and thousands of industrial users across the West, the average flow is down 17 percent a year compared to the 20th century average. Up to half of that missing flow is driven by human-caused climate change, Udall says.

Just last week, a team published a paper in Science showing that the Colorado’s flow is projected to diminish another 20 to 30 percent by the middle of the century, ratcheting up the pressure on every single user of the river water and intensifying the need to develop new, innovative solutions. Currently, the seven states that rely on Colorado River water are discussing ways to reduce their usage, both to deal with the fact that the river has been significantly overdrawn for years and to come up with a plan to adapt to a drier future.

Richter and his colleagues point to one potential action that could help keep water in the rivers, at least in the short term: paying farmers to not farm, a strategy called fallowing.

In places like the Imperial Irrigation District in inland Southern California, water managers needed to figure out how to keep local farmers’ water use extra low—so they paid them to let their fields go unplanted. Richter and his colleagues did the math and figured out that if 20 percent of the cropland currently used for cattle feed in the upper part of the Colorado River basin were to lie fallow, the states involved could meet their water use goals. In the drier, hotter lower river basin, fallowing almost half of the fields devoted to cattle feed might let the states meet their goals—but more changes would likely also be necessary.

“When you layer on climate change with the other issues the rivers are already facing, you end up with a double or a triple whammy,” says Xenopoulos, the fish ecologist. “We should be worried. This should be a wake-up call.”

But, she stressed, some parts of the water challenge posed by beef and dairy consumption can be addressed directly, today, and help to save fish and ecosystems.