Click the link to read the article on the Inside Climate News website (Wyatt Miskow):

September 15, 2025

A new report finds that Lakes Mead and Powell, the nation’s largest reservoirs, could store just 9 percent of their combined capacity by the end of next summer.

Consumption of Colorado River water is outpacing nature’s ability to replenish it, with the basin’s reservoirs on the verge of being depleted to the point of exhaustion without urgent federal action to cut use, according to a new analysis from leading experts of the river.

The analysis, published Thursday [September 11, 2025], found that if the river’s water continues to be used at the same rate and the Southwest sees another winter as dry as the last one, Lakes Mead and Powell—the nation’s two largest reservoirs—would collectively hold 9 percent of the water they can store by the end of next summer. After enduring decades of overconsumption of the river’s water, the lakes would have just under 4 million acre feet of water in storage for emergencies and drier years when demand can’t be met. Every year, roughly 13 million acre feet is taken from the river for drinking water and human development across the region, with conservative forecasts estimating roughly 9.3 million acre feet of inflow next year. 

The report is stark in its assessment of the situation: Current Colorado River levels require “immediate and substantial reductions in consumptive use across the Basin” or Lake Powell by 2027 would have no storage left and “would have to be operated as a ‘run of river” facility” in which only the inflow from the river could be released downstream. 

“The River recognizes no human laws or governance structures and follows only physical ones,” the report’s authors wrote. “There is a declining amount of water available in the Colorado River system, primarily caused by the effects of a warming climate—longer growing seasons, drier soils, and less efficient conversion of the winter snowpack into stream flow. Although American society has developed infrastructure to store the spring snowmelt and make that water available in other seasons to more completely utilize the variable runoff, the Colorado River watershed produces only a finite volume of water, regardless of how many dams exist.”

The lifeblood of the American Southwest, the Colorado River’s water flows from Wyoming to Mexico, enabling the region’s population and economies to develop. The damming of the river has diverted water to booming metropolises like Los Angeles and Phoenix while also supporting the U.S.’s most productive agricultural areas and powering some of the its largest hydroelectric dams. In total, the river supplies seven states, 30 tribes and 40 million people with water.

The compact that divvied up the river’s water a century ago overestimated how much actually flowed through it, and climate change has diminished the supply even further. The melting snowpack that runs off mountains in the spring to feed the river has declined, shrinking the river and its storage reservoirs during decades of drought. The seven states that take Colorado River water are divided into two factions engaged in tense conversations about its future and how cutbacks should be distributed. Current guidelines for managing the river in times of drought are set to expire at the end of next year, and new ones are legally required to take their place, but negotiations between states, tribes and other stakeholders over the sharing of the necessary cuts in water usage are at an impasse. 

But if current conditions persist, further cutbacks on the river won’t be able to wait until those negotiations are finished, the report’s authors find, and they urged the Department of the Interior “to take immediate action.”

“Let’s hope that we are all wrong and that it snows like hell all winter and runoff is wonderful and we buy ourselves some time and additional buffer,” said Kathryn Sorensen, director of research for Arizona State University’s Kyl Center for Water Policy and one of the report’s co-authors. “But of course, it never makes sense to plan as if it’s going to snow, and we have to deal with what is a realistic but not worst-case scenario and take responsible actions.”

Adding to the issue is the status of the infrastructure that enables the river to be diverted and stored for use. For example, the researchers write, it was thought that anything above what’s known as “dead pool”—a water level below the reservoirs’ lowest outlets that can pass water through the dams—was “active storage.” But testing last year from the Bureau of Reclamation, the federal agency overseeing the river and its dams, found that those outlets can only be safely used at water levels higher than previously thought and cannot be used for long durations.

Margaret Garcia, an associate professor at ASU’s School of Sustainable Engineering and the Built Environment, who was not a part of the study, said the analyses makes clear the “reality of dead pool is within sight” for the basin’s reservoirs, even without considering the possibility of having an extremely dry year.

She likened the reservoirs to having a savings account with a bank. “When you have a savings account, you have some time to scramble and figure things out,” Garcia said. “But if you’ve already drawn down your savings account and then  [you’re laid off] and you never filled it back up at least a little bit, you’re in for a really tough situation.”

And just like a savings account, Garcia said, a reservoir isn’t much good if it can’t generate hydropower or store water. 

Sorensen said the secretary of the Interior, Doug Burgum, has broad authority to act to protect critical infrastructure in both of the river’s basins. The question is what those actions should be.

“The solutions are there,” she said. “The solutions are known. They’re just extraordinarily painful to implement. “

State negotiators have worked this year to determine how to manage the river after 2026, Sorensen said, but the buffer of water stored in reservoirs “that we’re relying on to kind of get us through the negotiations and these difficult times is potentially much smaller than maybe was commonly understood.”

“No one comes out of this unscathed,” she said.