Click the link to read the article on the Aspen Journalism website (Heather Sackett):

April 1, 2025

Time is ticking for states that share the shrinking Colorado River to negotiate a new set of governing rules. One major sticking point, which has the potential to thrust the parties into a protracted legal battle, hinges on differing interpretations of a few sentences in a century-old agreement. 

In a recent letter, the river’s Lower Basin states – California, Nevada and Arizona – asked federal officials to analyze the effects of a hypothetical legal concept known as a “compact call.” 

The problem? The 1922 Colorado River Compact says nothing about a compact call. And although the phrase often looms like a threat over Colorado River discussions, there is no agreed-upon definition of the term, what would trigger a compact call nor how one would play out. In fact, the Upper Basin states – Colorado, New Mexico, Utah and Wyoming – don’t believe the laws governing the river even contemplate it.

The February letter comes as water managers from all seven Colorado River Basin states are in the midst of deciding how Lake Powell and Lake Mead will be operated and cuts will be shared after 2026 when the current guidelines expire. In March 2024, each basin submitted competing proposals to the U.S. Bureau of Reclamation. In January, federal officials with the outgoing Biden administration released their analysis of five different potential ways forward and did not include either basin’s proposal, but a “basin hybrid” that incorporated elements from both. 

In essence, the Lower Basin states have identified a potential opening with the Trump administration, and asked new leaders at the Interior Department to adopt the Lower Basin’s view on some of the most contentious and disagreed-about parts of Colorado River management.

“I believe that under the law, the compact requires delivery of 7.5 million acre-feet of water on a 10-year rolling average, plus one-half of the Mexico Treaty obligation to the Lower Basin,” said Tom Buschatzke, director of Arizona’s Department of Water Resources. “So we want to see Reclamation, as our request indicated, incorporate that outcome into the modeling for any alternative to look at. That includes how reductions in the Upper Basin states might have to occur.”

Over a century ago, the compact split the river’s water evenly, with half (7.5 million acre-feet a year) going to the Upper Basin and half to the Lower Basin. Another 1.5 million acre-feet a year was later allocated to Mexico.  

The crux of the dispute comes from how the Upper Basin states and the Lower Basin states each interpret a key phrase in the compact: “The States of the Upper Division will not cause the flow of the river at Lee Ferry to be depleted below an aggregate of 75,000,000 acre-feet for any period of ten consecutive years…”

To the Upper Basin states, “will not cause” means that their use won’t be the reason the Lower Basin doesn’t get its allocation. They see it as a “non-depletion” obligation. 

According to Colorado officials, they’re not delivering water downstream, but rather  they’re not causing the flows to be depleted. 

“What this means is that if the flows were to drop below 75 million acre-feet over a ten-year period, there would be an inquiry into what caused that to occur,” Michael Elizabeth Sakas, Colorado River communications specialist with the Colorado Water Conservation Board said in a written response to questions from Aspen Journalism.  

On the other hand, the Lower Basin states say they’re owed the water, with the Upper Basin states required to send the 75 million acre-feet over 10 years, plus half of the Mexico Treaty obligation (which works out to 82.5 million acre-feet every 10 years) downstream to the Lower Basin. 

Compact “tripwire” threatens to complicate

Colorado River expert Eric Kuhn says that the latest report from the U.S. Bureau of Reclamation is a major caution sign for the basin. An anemic snowpack this past winter could be setting the basin on the road to a compact call (as defined by the Lower Basin). The most recent federal forecast predicts that in 2027, the 10-year cumulative flow at Lee Ferry could drop below 82.5 million acre-feet, a threshold Kuhn calls the first “tripwire” for a compact call. 

“If flows were to go below 82.5 million, then that’s the first time, in theory, the lower division states could point to the Upper Basin and say, ‘You’re not complying with your compact obligations,’” Kuhn said. “This is not going to sneak up on us. I think most of the modeling shows that it’s almost inevitable we will drop below 82.5 in the next three or four years.” 

But Upper Basin officials disagree. In their interpretation, this tripwire doesn’t exist. A compact call is a concept recognized only by the Lower Basin. 

They also point out that calls for water apply to situations where there is a senior rights holder and a junior rights holder. Under the prior appropriation system, the oldest water rights get first use of the river, and senior rights can force junior rights to stop using water so seniors can get the full amount they are entitled to. But Upper Basin officials say there is no priority between the two basins; they are on equal standing. [ed. emphasis mine]

That may be true, but the three Lower Basin states are also home to the basin’s biggest water users and cities, with more political power than the sparsely populated Upper Basin states.

River headed for “wildly uncharted territory”

So what would happen if and when the river shrinks enough to trigger the first compact tripwire?

In practice, a compact call could mean the Lower Basin states would sue the federal government to get them to send more water downstream from Lake Powell. (The U.S. Bureau of Reclamation is responsible for making releases from Lake Powell and Lake Mead.) The Lower Basin states could also demand that the Upper Basin states implement cuts to get more water into Lake Powell. But the Upper Basin states will almost certainly argue they are in compliance with the compact and don’t need to make cuts. The Supreme Court could then decide whether the Upper Basin states are in compliance with the compact.

“It’s wildly uncharted territory,” said Chuck Cullom, the executive director of the Upper Colorado River Commision. “It’s not a straightforward path to say: ‘We need you to release more water out of Glen Canyon Dam and curtail uses.’”

The Upper Basin’s argument hinges on what is causing the flows at Lee Ferry to drop. The four states say it’s not their fault, because they only use between 3.5 and 4.5 million acre-feet a year, far less than their allocation of 7.5 million acre-feet. The culprit, they say, is climate change, which according to scientists has contributed to a 20% decline in flows from the 20th century average. They have also shown that every 1 degree Celsius of warming results in a 9% reduction in flows. 

With a fixed number for how the river is shared, and a slowly dwindling amount of water available, the Upper Basin has been bearing the brunt of the effects of climate change, a phenomenon that Kuhn calls the “Upper Basin squeeze.” But the climate change argument could open a can of worms.

“There are numerous other water compacts between states,” Kuhn said. “Are we reopening every one of those? It could mean that other states do not have to comply with their compact obligations.That would be a precedent decision that would affect every compact in the western United States.”

How would cuts work?

Water users on Colorado’s Western Slope are eager to know how cuts could play out and over the past few years they have asked state officials repeatedly for more clarity on this issue. One reason is because most of the big transmountain diversions that take water from the mountainous headwaters of the Colorado to Front Range cities date to after the 1922 compact, meaning they would likely be cut first. But as the population centers and economic engines of the state, it’s unlikely a plan to cut water use would include turning off the taps to Denver.  

In a crisis situation where cuts are mandatory, the strict prior appropriation system would probably not hold.

“They’re going to have to make hard decisions, and they are going to primarily meet the human health and safety needs of people first,” Kuhn said. “It’s an open secret that the priority system works under normal conditions; it doesn’t work in emergencies.”

Western Slope water users also want to know the state’s plan for cuts, because some areas may be more at risk of forced cutbacks than others. The Yampa/White/Green River basin in the northwest corner of the state, for example, developed later than other places, with lots of more junior water rights. Would they be first on the chopping block? 

“We believe that regardless of where things stand on the river, clarity can’t hurt water users,” said Peter Fleming, general counsel with the Colorado River Water Conservation District. “In the long run, clarity will help people to plan better.”

But state officials have been reluctant to provide clarity about how cuts could be implemented, saying now is not the time to plan for it and that the Upper Basin states have always been in compliance with the compact.

“Colorado is not at risk of any compact curtailment scenario in the near future,” Sakas said in a written response to Aspen Journalism. “For the last 20 years, the Upper Basin has been using half of what we are allowed to use under the 1922 Compact while our downstream neighbors use significantly more than their apportionment.”

Figuring out who would be the first to take cuts and tracking that water to the state line would not be an easy task, said Colorado River expert Jennifer Gimbel. Gimbel is the senior water policy scholar at the Colorado State University Water Center and is the former director of the Colorado Water Conservation Board. 

“It would be a tremendous headache and a huge undertaking,” she said. “But I don’t know if that means we shouldn’t be doing it.”

The Colorado Division of Water Resources, in a first step, has been developing measurement rules and requiring measurement devices for water users across the Western Slope. According to state officials, the goal of this effort is to accurately measure diversions so that if necessary, Colorado sends downstream only the water that is required to maintain compact compliance and not a drop more. 

Trying to stay out of court

One thing most water managers agree on is that finding a seven-state consensus is better than the potentially protracted litigation possible under some kind of compact call scenario. Some are hoping for the best but preparing for the worst. The Arizona Department of Water Resources requested about $1 million last year for Colorado River litigation from the state budget. Buschatzke said the Upper Basin states might fare worse under a compact call than they would by adopting the Lower Basin proposal.

“Because there are a lot of moving parts, litigation — a compact call — is a possibility,” he said. “It’s not a possibility I want to see occur. But I’ll have to do what I have to do to protect the state of Arizona.”

If the states can come up with new guidelines that fairly share the river, the threat of a compact call, which has long hung over Colorado River management discussions, could evaporate like water from the surface of Lake Mead. Cullom said that in 2007 when the seven states implemented the soon-to-expire guidelines that are currently in place, they agreed that if the two basins made good on their commitments outlined in those guidelines, they would set aside the issue of compact compliance — at least until after 2026.

“If they can figure out a way to live within the means of the river in such a manner that both the Upper Basin and Lower Basin agree, hopefully addressing a compact call again won’t be needed because it’s been addressed,” Gimbel said. 

This story was produced by Aspen Journalism, in partnership with The Water Desk at the University of Colorado’s Center for Environmental Journalism.