The Colorado River irrigates farms, powers electric grids and provides drinking water to 40 million people. But as its supply dwindles, a crisis looms.

Published August 21, 2021

For farmers in the deserts of central Arizona, success and failure is defined by who has water and who does not. At the moment, Dan Thelander is still among the haves.

Inside a municipal building in Pinal County, Thelander rolls a map out across the board room table.

On the patchwork of brown desert and green farmland in front of us, Thelander points out the parcels of land where he and his brother, son and nephew grow cotton, alfalfa and several other crops.

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Second-generation farmer Dan Thelander stands by a new sprinkler system in one of his alfalfa fields in Maricopa, Arizona. Caitlin O’Hara for CNN

About half the water he uses to irrigate his land is pumped out of ancient aquifers deep beneath the desert floor. The other half, however, originates hundreds of miles away at the headwaters of the Colorado River.

Today, this river system supplies 40 million people in seven western states and Mexico, and irrigates more than 5 million acres of farmland on its way into Mexico and the Gulf of California.

Las Vegas relies on the river for 90% of its water supply, Tucson for 82% and San Diego for around 66%. Large portions of the water used in Los Angeles, Phoenix and Denver also come from the river, and experts say these booming metropolises would not have been possible without its supply.

But a crisis is unfolding, and farmers, scientists, water managers and policy makers across the Southwest are increasingly alarmed.

Water managers have long recognized that the river is plagued by overuse. But over the last two decades, demand for the river’s water has often outstripped its supply. Since 2000, the river’s flows have shrunk by roughly 20% compared to the 20th century average, due in large part to the human-caused climate crisis. At the same time, its two main reservoirs — the savings account for the entire system in times of drought — have drained rapidly.

Lake Mead — the largest manmade reservoir in the US, which is fed by the Colorado River — recently sunk to its lowest levels since the lake was filled in the 1930s. Its water levels have fallen more than 146 feet since their peak in January of 2000, and the lake is now just 35% full. Lake Powell, the river’s second largest reservoir, sits at 32% of its capacity. As water levels drop, billions of kilowatt hours of hydroelectricity that power homes from Nebraska to Arizona are also at risk.

Lake Mead water levels fall to 35% full over 21 years

2000

2000 satellite image of Lake Mead. The desert surrounds the reservoir.

2021

2021 satellite image of Lake Mead. The difference is striking as the Lake edges retreats over 21 years.

Composite imagery from NASA/USGS

“We’re in uncharted territory for this system,” says Jeff Lukas, an independent consultant and former research scientist at the University of Colorado at Boulder, where he focused on water issues for 20 years.

On Monday, the US Bureau of Reclamation declared the first-ever official shortage, which will trigger the largest mandatory water cuts to date in the Colorado River Basin. And after decades of receiving water from the Colorado River, the spigot could soon be turned off on many farms here, including Thelander’s.

While the farmers knew this day would come, a harsh reality is setting in: To stay in business, they’ll need to pull more water from below ground.

Back on the table, Thelander points to the diamonds and circles that dot the map. Those mark the locations of new groundwater wells that his irrigation district is considering — the first new ones they have drilled in decades, Thelander says.

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Thelander points to a map of canals and groundwater pumps in the Maricopa-Stanfield Irrigation and Drainage District. Caitlin O’Hara for CNN

For much of the last century, Colorado River management has focused on choosing who will be allowed to stick their straw into the river next and how much water they can take. At times, that process has sparked major disputes — with some leading all the way to the US Supreme Court.

Now, many of the basin states are having a more painful discussion: deciding who will receive less water — and how much. Experts say the next phase in the river’s history could be even more contentious.

The current Colorado River guidelines expire in 2026, and early negotiations are already getting underway for a new framework to determine how to divvy up its water. But by the time officials from the states, Mexico, Native American tribes and the federal government convene, it is likely that the river’s water supply will be even more tenuous than it is today.

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Thelander utilizes drip irrigation for his cotton fields in Maricopa, Arizona. Caitlin O’Hara for CNN

Scientists and water policy experts say that the science is clear: The Colorado River’s supply will likely shrink further as the planet warms. Given what we know, many say we will have to use even less water in the future.

But will the states be able to agree to new guidelines that reflect this reality? And with the Southwest’s growing urban centers and farms both reliant on the river’s supply, who will be willing to take less water?

How elected officials and water managers answer those questions will decide the fate of the most important water resource in the American West — and the millions of people who rely on it.

The roots of this current water crisis can be traced back nearly 100 years to the signing of the Colorado River Compact.

In November of 1922, with then-Secretary of Commerce Herbert Hoover overseeing the deliberations, delegates from all seven Colorado River Basin states convened in Santa Fe, New Mexico, to hammer out the guidelines.

From the start, the compact negotiations were contentious. Squabbles erupted over details big and small, from how to measure the river’s flow to how to portion out its supply.

Efforts to reach a deal began in January of 1922 and resumed in November, when delegates from the states gathered in Santa Fe, New Mexico. After two weeks of deliberations, they finally reached an agreement on November 24, 1922.

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Then-Secretary of Commerce Herbert Hoover presiding over the 1922 signing of the Colorado River Compact. US Bureau of Reclamation

From the Southwest’s cities to its farms that feed the world, water managers say much of what we see today would not exist without the dams, canals and pipelines that the compact paved the way for.

“[The Colorado River] is the lifeblood of the American Southwest,” says Jeff Kightlinger, who led Southern California’s Metropolitan Water District for 15 years before his recent retirement. “None of these cities would be possible but for the Colorado River and the development of it for all of these regions.”

Over the course of the 20th century, new agreements and court decisions further divided up the river’s supply among the seven basin states, Mexico and the region’s Native American tribes. But there was a serious flaw in the original compact — one that, in part, explains why the river is facing its first-ever shortage today.

When the delegates met, they agreed to give the Upper Basin (made up of Colorado, Wyoming, Utah and New Mexico) and the Lower Basin (California, Arizona, and Nevada) each 7.5 million acre-feet of water to use on an annual basis.

Those portions were based on estimates that the river’s flow totaled roughly 16.4 million acre-feet each year. That was more than enough to meet the demands of the states. However, data shows those estimates exceed the amount of water the river actually provides in most years.

Analysis of US Bureau of Reclamation (USBR) data shows that between 1906 and 2019, annual flows on the river actually averaged just under 14.8 million acre-feet. Over the last two decades, flows have been even lower — just an estimated 12.3 million acre-feet on average each year.

Up until the 1990s, the Lower Basin states were not using all the water they were entitled to on paper. This allowed officials to let the river’s water accounting problem persist for decades, experts say.

“Through the 20th century, it was easy for political actors to ignore that reality …,” says John Fleck, a professor at the University of New Mexico who has written several books on the Colorado River and water issues in the West. “There was slack in the system because it took us a century to build all the dams and diversions that people dreamed about in the 1920s.”

As water rights were granted and new canals were built, that slack has gradually disappeared.

Data shows that the over-allocation problem became more apparent in the years after one of the last big straws was inserted into the river.

The Central Arizona Project (CAP) — a massive, 336-mile canal and pipeline system that carries Colorado River water across the desert to Phoenix, Tucson and farms and towns in between — was authorized by Congress in 1968.

Before the CAP was completed in the 1990s, heavy groundwater pumping in central Arizona was sucking aquifers dry at an alarming rate. The CAP promised a renewable, reliable source of water.

With no infrastructure to deliver Colorado River water to cities in the middle of the state, Arizona was also only using about half of its Colorado River allocation before the CAP was completed, according to Ted Cooke, the general manager of the CAP.

California had long opposed the project, so to gain support from the state’s congressional delegation, Arizona made a key concession: That in the event of a shortage, fulfilling California’s water deliveries would take priority over meeting the needs of CAP water users.

Now, with water cuts looming next year, the CAP’s status in the Colorado River’s pecking order is proving significant.

Arizona farmers like Dan Thelander have known for years that their supply of Colorado River water would eventually be phased out. They just didn’t expect it to happen so soon.

A drought that began more than two decades ago, along with the effects of higher temperatures due to global warming, have rapidly sapped the river’s flow. And in the long-term, scientists and water policy experts say those problems pose a threat to users far beyond the farms of Pinal County.

Droughts are temporary. The drying up of the river may not be

Rain evaporates near an irrigated cotton field in Casa Grande, Arizona. The area has been experiencing a “megadrought.” Caitlin O’Hara for CNN

The Colorado River’s drainage basin spans some 246,000 square miles but most of its flow originates in a handful of snow-capped mountain ranges in southern Wyoming, western Colorado and northeastern Utah, according to Jeff Lukas, the research scientist and water consultant.

The river flows through some of the country’s most arid land, so the snow that accumulates in those areas is critical. In most years, snowmelt is responsible for about 80% of the river’s water supply, Lukas says.

Many scientific studies have examined why there is less water flowing into the river. Nearly all have found the fingerprints of human-caused climate change.

The first, and perhaps most cited, explanation is the ongoing “megadrought,” which began in the year 2000.

A study published in the journal Science in 2020 found that the period from 2000 to 2018 was the driest stretch the Southwest has experienced since the 1500s, and that nearly half of the drought’s severity could be attributed to global warming.

“When you have more evaporation, you have less water left over to come down the river.”

Chris Milly, US Geological Survey

As dry as it has been, the study found that this may only be the beginning. Past megadroughts have lasted longer than the current one.

But a lack of snow and rain doesn’t fully explain what is happening to the Colorado River. And droughts, after all, are temporary. Some scientists say the evidence shows the river’s shrinking supply is likely not so fleeting.

Brad Udall, a climate scientist at Colorado State University, argues the river’s plight is best summed up by another term: aridification.

Broadly speaking, aridification is a shift to a new climate state dominated by water scarcity and driven by the effects of hotter temperatures. Temperatures across the basin have risen by an average of 1.4 degrees Celsius (2.5 degrees Fahrenheit) over the last century.

“[Warmer temperatures] are just this constant, year in and year out, force on the system,” Udall says.

As temperatures warm, the amount of precipitation that falls as snow decreases, and the snow that does fall melts earlier, according to Chris Milly, a hydrologist with the US Geological Survey who co-authored a study last year examining the river’s decline.

Snowpack reflects much of the sun’s energy back into space. But as the snow melts earlier and leaves behind exposed soil, more heat from the sun is absorbed by the ground. This leads to more evaporation, which means less runoff ends up in the river, Milly said.

“Evaporation is how the river basin cools itself,” Milly says. “When you have more evaporation, you have less water left over to come down the river.”

Dry soils and thirsty plants also contribute to the problem. When soils are parched by high temperatures in the summer and fall months, it can lead to runoff reductions that persist even a year later, Udall says.

Higher temperatures also mean that the atmosphere is “thirstier” and capable of holding more water. This increases evaporative losses from soils and water bodies.

Over the last year, Udall says we’ve seen how some of these processes can lead to alarmingly low runoff and stream flows.

All of this points to an unpleasant conclusion, Udall says: As long as humans fail to halt global warming, it’s likely that there will be even less water in the river in the future.

A 2020 study in the journal Science co-authored by Milly tried to approximate how much less. The authors found that further decreases in the river’s flow are likely no matter what actions are taken. But without any significant cuts to greenhouse gas emissions, the study found the river’s flows could shrink by as much as 31% by the middle of this century.

“It’s possible you might have a wet year, but the long-term trend is in completely the wrong direction,” Udall says. “Every passing year that becomes clearer, and it’s getting harder for anyone who thinks otherwise to be taken seriously.”

Beneath a drill rig towering high above the desert floor, two men in yellow hard hats pull levers to drive a massive metal pipe into the ground.

Feet away, a deafening machine called a shaker vibrates violently, separating muddy drilling fluid from chunks of earth pulled loose by the drill bit as it punctures layers of clay, sand and gravel on its way down.

It’s a scene you might expect to see in the vast oil fields of the Permian Basin.

But here, surrounded by acres of alfalfa and dairy pens on the outskirts of Maricopa, Arizona, the men are looking for something more valuable to the local economy: water.

To pump water up from the aquifer below, the men will have to drill down between 1,200 and 1,300 feet, according to Marty Weber, the CEO of Weber Water Resources, the company responsible for drilling this well.

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A new groundwater well is drilled on the outskirts of Maricopa, Arizona. Drew Kann/CNN

This one is being paid for by the Maricopa-Stanfield Irrigation and Drainage District, with money given to the farmers by the state of Arizona and the CAP as part of their agreement under the state’s drought contingency plan. Drilling these wells is part of the farmers’ strategy to survive the cuts that are coming to their Colorado River water supply.

Next year farmers in Thelander’s district will only get about 1/3 of the water supply they’ve received in past years. But in 2023, Pinal County’s farms will likely see their Colorado River supply dry up completely, according to the state’s drought plans.

“… any way you cut it, our farm will be less profitable.”

Dan Thelander, Tempe Farming Company

Before the cuts take effect on January 1, 2022, Thelander hopes they will have nine to 10 new wells to make up some of the water they stand to lose. The new wells are just one sign of the changes coming soon to the county. Soon, there will be fallow fields, too.

Right now, Thelander’s crops are doing well. But next year, he expects to leave 30% to 40% of his land unsown.

“Like anybody in business, when you’re faced with adversity, you just knuckle down and do the best you can,” he says. “But any way you cut it, our farm will be less profitable.”

While the desert heat is ideal for growing cotton, the county is also a dairy powerhouse. At one point, Pinal County ranked in the top 1% of all US counties for both cotton and milk sales, according to a 2018 study by economists at the University of Arizona.

Many farms here, like Thelander’s, specialize in growing alfalfa, corn and other crops to feed the thousands of dairy cattle on local farms.

Consumers in Phoenix likely won’t notice a difference when the water cuts kick in, says George Frisvold, a professor at the University of Arizona and a co-author of the 2018 study. But in the local farming economy, he expects there will be significant pain when the cutbacks take effect.

“You’ll have these ripple effects through the economy, and jobs go away.”

George Frisvold, University of Arizona

The same 2018 University of Arizona study found that under a scenario where farms here lose all of the Colorado River water allocated to them, it could cost the county between $31.7 and $35 million and as many as 480 jobs.

“You’ll have these ripple effects through the economy, and jobs go away,” Frisvold says. “In smaller, rural areas in Pinal County, it’s going to be more noticeable.”

Jim Boyle, a dairy farmer who milks around 3,500 cows on his farm near Casa Grande, Arizona, says that he too will likely have to fallow some of the land where he grows feed for his cattle.

And while he says he is fortunate to have deep, productive groundwater wells on his property, he is concerned about how others whose livelihoods are tied to farming will fare.

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Dairy cows are seen at fourth-generation farmer Jim Boyle’s farm. He plans to transition into having mostly Jersey cows because their smaller size means they do better in the Arizona heat and require less water and feed. Caitlin O’Hara for CNN

“There are a lot of ag-related businesses in our county — the tractor sales guys, the machinery guys, the fertilizer and chemicals guys,” Boyle says. “It will have a roll-on effect throughout the county … and I think there’s some worry out there.”

There is also concern from some in the state about the farmers’ return to heavy groundwater pumping.

Before the CAP began delivering water to Pinal County’s farms in the late 1980s, farms here were totally reliant on groundwater to irrigate their crops. But pumping was depleting the aquifers faster than they could be replenished, causing huge fissures to form across the county as the ground sank.

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Boyle and his son James look over the Hohokam canal at the family’s dairy farm in Casa Grande, Arizona. The canal connects to the Central Arizona Project. Caitlin O’Hara for CNN

Already, projections show there is not enough groundwater available to meet future demands in the Pinal County Active Management Area (AMA) — which includes much of Pinal County, as well as parts of Maricopa and Pima counties — according to an Arizona Department of Water Resources spokesperson. Last month, Tom Buschatzke, the director of the Arizona Department of Water Resources (AZDWR), told leaders in the AMA that “the days of utilizing native groundwater for development in Pinal are over, it’s done.”

Still, with their Colorado River water on the verge of disappearing, farmers here are planning to pump even more groundwater to irrigate their fields.

“I am concerned about Pinal turning to groundwater because that means there won’t be resources for future use,” says Sarah Porter, the director of the Kyl Center for Water Policy at Arizona State University. “It’s like spending your long-term savings — you want to do that very advisedly.”

Whether the loss of Colorado River water will accelerate other trends in the county remains to be seen.

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Solar panels are seen across from Caywood Farms in Casa Grande. Caitlin O’Hara for CNN

Nancy Caywood’s farm near Casa Grande used to get water from the San Carlos reservoir in Eastern Arizona, part of the Gila River system. The reservoir ran dry in April and she says her farm hasn’t received water since.

To make ends meet, Caywood and her son, Travis Hartman, are growing corn on leased land that has access to Colorado River water. The money Hartman makes from that crop should help him keep the family farm, he says.

But next year, farming there may no longer be an option, as cuts to Colorado River water hit the county.

Already, Caywood’s 255-acre farm is flanked to the East by a large solar installation, and she says the farmland across the street could soon have panels installed.

She says that they too have been approached before about leasing their land to solar developers, but ultimately decided against it.

As the drought continues, she admits it is getting harder to tell them “no.”

“We’ve just decided we’ll try to hang on and farm as long as we can,” she says.

Nearly a century has passed since Herbert Hoover led the first attempt to divide up the Colorado River’s supply.

But as the first mandatory water cuts loom, authorities in states across the basin say that they are preparing for a future with less water.

For years, states like Arizona have been “banking” water from the Colorado River in aquifers. Las Vegas will phase out “nonfunctional grass” by 2027 in an effort to save precious water. And across the Southwest, cities are investing in wastewater treatment and reuse. All of this, they say, will allow their economies to thrive, even if the river’s supply shrinks.

But what the next 100 years look like hinges on negotiations that are beginning to take shape now.

Kightlinger, the recently retired general manager of California’s Metropolitan Water District and a veteran of past river negotiations, says he expects the 2026 process will be painful.

“We had very intense, difficult negotiations in 2003 and 2007 and again in 2019. But this is going to be the hardest one yet.”

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An aerial view of the Red Rock Country Club in Las Vegas, where much of the grass turf, lakes and ponds have been been removed to save water and earn rebates from the Southern Nevada Water Authority. Roger Kisby/Redux

A failure to reach an agreement could usher in an era of uncertainty for the basin’s 40 million water users and increase the likelihood of legal conflicts, says John Entsminger, the general manager of the Southern Nevada Water Authority, which provides water from the Colorado River to nearly 2.3 million people in Las Vegas and across the state.

The drought contingency plans that were inked in 2019 between the federal government, the states, Native American tribes and other water users have, so far, staved off a worst-case scenario — like an emptied Lake Mead or Lake Powell. Entsminger and others pointed to those past negotiating successes and expressed confidence that they could reach a new deal.

“The Colorado [River] has been described as the most litigated river in the world, and I think that’s true if you’re talking about the60s and 70s,” Entsminger says. “But since the mid-’90s, this has been the most successful river basin in the world in terms of seven states and the country next to it coming together and … figuring out how to make this river work for everyone.”

One of the biggest challenges experts say negotiators must face is how to handle the large amount of water used by agriculture, which is responsible for around 70% of water use across the basin.

Pinal County’s farmers are bearing the brunt of the first round of water cuts because of their low position in the state’s water priority system. But there are other farming centers, in Arizona and elsewhere, which possess some of the highest priority water rights in the entire basin.

One of those places is Yuma, Arizona, the river’s last stop in the US before it flows into Mexico. Part of “America’s Salad Bowl,” around 90% of the leafy greens produced in the US in winter are grown on Yuma’s farms, according to the county’s chamber of commerce.

Under current law, the entire Central Arizona Project could go dry before Yuma’s farms lose a drop of water, due to their high priority water rights, according to AZDWR director Tom Buschatzke.

Buschatzke said that the US and the world need the healthy, high-value crops that they grow in Yuma, but acknowledged that the river’s shrinking supply may force difficult tradeoffs.

“Certainly, the community of Yuma does not want to see any of the water that goes to those farms go to non-agricultural purposes, but that is something that is certainly on the radar screen,” Buschatzke says.

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Farm workers harvest and package cauliflower near Yuma, Arizona. Jon G. Fuller/VWPics/AP

Tom Davis, the general manager of the Yuma County Water Users Association, says that with less water to go around, he expects there will be new pressure to shift agricultural water supplies to the Southwest’s growing cities.

He says he and the farmers he represents will fight to “the bitter end” to protect their water rights, but recognizes that they are not untouchable.

The water rights of many Native American tribes, whose ancestors have farmed across the region for thousands of years, are also among the highest priority in the entire basin. Today, 22 of the 30 federally recognized tribes in the region have rights to an estimated 22 to 26% of the river’s water supply, according to recent analysis from the Water and Tribes Initiative, an alliance dedicated to tribal water issues.

But despite holding a sizeable portion of the pie, many tribes have been left out of these types of negotiations in the past. However, there are signs that this is changing in parts of the basin.

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Eugene Boonie, who is from Navajo Nation, fills up his water tank at the livestock water spigot in Gap, Arizona. Navajo land spans 27,000 square miles in Arizona, New Mexico and Utah, and like many other Native American tribes in the Colorado River Basin, there are unresolved water rights claims on their land. Stephanie Keith/Reuters

The Gila River Indian Community, located south of Phoenix in Maricopa and Pinal counties, now holds the single largest water allotment in the entire Central Arizona Project system, thanks to a 2004 settlement brokered with the federal government.

The Gila River Indian Community’s governor, Stephen Roe Lewis, says he had to fight for a seat at the table in the negotiations over the 2019 drought contingency plan. But once there, he played a key role in helping push the deal across the finish line in Arizona.

Now, as talks for the new 2026 guidelines begin, he says he plans to vigorously defend his community’s water.

“If we’re treated as sovereign tribal entities and with respect towards our individual water histories, then I’m looking forward to being a part of the process.”

As stakeholders prepare to protect their water supplies, plans to use even more river water are also forging ahead in some corners.

“The Lake Powell pipeline is a symbol of our archaic, unsustainable water policy of the 20th century.”

Zachary Frankel, Utah Rivers Council

The most controversial new diversion is Utah’s proposed Lake Powell pipeline, which would pump Colorado River water from near Glen Canyon Dam in Arizona roughly 140 miles to the city of St. George, Utah, and surrounding towns. Critics say the project represents a denial of the realities of climate change that could imperil the water supplies of millions.

“The Lake Powell pipeline is a symbol of our archaic, unsustainable water policy of the 20th century,” says Zachary Frankel, executive director of the Utah Rivers Council. “… Utah is still in this fantasy pretending that climate change isn’t impacting our water supply, and it’s more than crazy — it’s irresponsible and reckless.”

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The bleached “bathtub rings” are visible on the rocky banks of Lake Powell at Reflection Canyon in Utah. They show where water levels used to be. Justin Sullivan/Getty Images

The project appeared to be on a fast track to approval under the Trump administration last year, but after the six other basin states sent a letter to then-Secretary of the Interior David Bernhardt opposing the pipeline, Utah requested an extension to consider their views and other public comments.

Despite their pushback, Utah’s new Colorado River commissioner Gene Shawcroft says he believes the project is important to the state’s growth and intends to push for its approval.

A potential new (and expensive) source of water

The Sea of Cortez is seen near Puertecitos, Mexico. Guillermo Arias/AFP/Getty Images

Meanwhile, as water levels in Lake Mead plummet, states are exploring opportunities to develop new sources of water — in addition to what they receive from the Colorado River.

Arizona is weighing the possibility of building desalination plants on the Sea of Cortez in Mexico to augment its water supplies.

“… when the supply that we’re depending on is dwindling, what else are you going to do?”

Ted Cooke, Central Arizona Project

If built, the plants would use reverse osmosis or thermal distillation to transform salt water into fresh. That water could be used in Mexico and in exchange, Arizona would potentially receive a portion of Mexico’s Colorado River water supply, according to AZDWR director Tom Buschatzke. While legal and diplomatic hurdles remain, Buschatzke said the rapidly deteriorating situation on the river has added new urgency to the effort.

Earlier this year, Arizona Governor Doug Ducey and Governor Claudia Pavlovich of Mexico’s Sonora state signed an agreement to study potential desalination sites. Last year, a feasibility study found the plants could cost in excess of $3 billion to build and cost between $71 million and $119 million annually to operate, not to mention the huge amounts of energy required to pull salt from water.

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A harvested corn field in Casa Grande is no longer being irrigated. Caitlin O’Hara for CNN

Still, with Arizona more vulnerable to water cuts than other states, Central Arizona Project General Manager Ted Cooke says everything must be on the table.

“It’s expensive, but when the supply that we’re depending on is dwindling, what else are you going to do?,” he says.

But new water sources are still years and billions of dollars away from becoming reality. As central Arizona prepares for painful water reductions and the possibility of deeper cuts in the next few years, the clock is ticking to conserve the supply millions rely on today.

With each passing month, new projections offer a glimpse further into the river’s future. The picture they paint is not pretty.

In June, new modeling showed there is a 17% chance that Lake Powell could sink so low by 2024 that hydroelectric generation at Glen Canyon Dam would become impossible. At full capacity, the dam can produce enough power for some 5.8 million homes. The loss of that electricity would add more stress to power sources in the West, which have shown vulnerability to blackouts in extreme heat amplified by global warming.

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Lake Powell’s plunging water level threatens Glen Canyon Dam’s capacity to produce hydropower. Justin Sullivan/Getty Images

To keep the generators running, the Bureau of Reclamation recently announced that smaller reservoirs in the Upper basin would release water to help prop up Lake Powell. The influx they’ll provide will raise water levels by around 3 feet. But for a lake that now routinely drops 4 feet or more in a month, it may not buy much time.

The future of Lake Mead also looks precarious.

The same models show a 1-in-5 chance that the lake could fall to 1,000 feet above sea level by 2025. That’s only 50 feet above the bare minimum needed to allow Hoover Dam to generate electricity and just 105 feet above “dead pool.” At dead pool, what little water is left behind cannot flow through Hoover Dam. Instead, it would have to be pumped out.

As water levels drop, new layers of the lake’s now-trademark “bathtub rings” are revealed. Today, the white mineral deposits left behind on the shoreline’s sandstone walls tower more than 140 feet above the boats below.

They are a reminder of wetter times, ones that occurred not so long ago.

They are also the most obvious sign of a river system, largely conceived in the 20th century, that is struggling to adapt to the harsh realities of climate change.

Graphics sources: US Geological Survey, National Hydrography Dataset, US Dept. of Agriculture (Colorado Basin boundaries); US Bureau of Reclamation (reservior levels and projections, natural flows, Colorado Basin supply and usage); Central Arizona Project (project location); 2007 Interim Shortage Guidelines, Lower Basin Drought Contingency Plan, Minute 323 between Mexico and the US, Binational Water Scarcity Contingency Plan, Congressional Research Service (water cuts for Lower Basin states and Mexico); NOAA, Colorado River Basin Forecast Center (soil moisture); US Dept. of Agriculture (snow-water equivalent, streamflow volume); Colorado River Compact of 1922, Boulder Canyon Act of 1928, US-Mexico Water Treaty of 1944, Upper Colorado River Basin Compact of 1948 (state water allocations)

Boaters pass Lake Mead’s “bathtub rings” in June. Water levels in the reservoir are the lowest they have been since the lake was filled after the Hoover Dam was completed in the 1930s. Allen J. Schaben/Los Angeles Times/Shutterstock

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