Wyoming’s share of the Colorado River may seem small on the map, but the legal and hydrologic pressure tied to the system is increasing, and the stakes for water users in the Green River and Little Snake basins are significant, according to Chris Brown, Senior Assistant Attorney General in the State of Wyoming’s Water and Natural Resources Division.

Brown spoke February 19 during the Wyoming Farm Bureau Federation Legislative Meeting about worsening shortages in the Colorado River Basin, the deadlock between upper and lower basin states and a Wyoming bill intended to create a voluntary conservation framework tailored specifically to the Colorado River.

“This is really kind of a unique program,” Brown said. “Something like this has never been tried before in Wyoming.”

River governance

Brown described the Colorado River as Wyoming’s most complex interstate river system. While Wyoming participates in seven interstate compacts and three interstate decrees, he said the Colorado is unique because it is governed by multiple major legal instruments and involves seven states plus Mexico.

At a high level, Brown explained the 1922 Colorado River Compact divided the river into two geographic regions — the upper basin and lower basin — and allocated 7.5 million acre-feet to each. An additional 1 million acre-feet was generally attributed to tributary use in the lower basin. A 1944 treaty guarantees Mexico 1.5 million acre-feet annually.

The 1948 Upper Colorado River Basin Compact then divided the upper basin share among Wyoming, Colorado, New Mexico and Utah by percentage. Wyoming’s share, Brown said, is 14 percent of the upper basin allocation.

Even by 1948, Brown noted, states recognized the 1922 compact relied on a wetter period of record and overestimated the long-term supply.

The core dispute

Brown said the central disagreement is how to interpret the upper basin’s delivery obligation at Lee Ferry, the compact accounting point. Lower basin states argue the compact requires a fixed annual delivery. Upper basin states disagree.

“We think it’s a conditional promise,” Brown said. “It depends on what’s going on.”

As flows have declined, Brown said the dispute has sharpened. He summarized the math driving the conflict: if the lower basin insists it is entitled to roughly 8.23 million acre-feet per year and Lee Ferry flows are around 11 million acre-feet, only about 3 million acre-feet remains for the entire upper basin. But the upper basin’s average annual use is about 4.5 million acre-feet.

The consequences for Wyoming under that interpretation would be severe, Brown said.

“As soon as you get to about a million acre-feet, Wyoming would lose all of the development that it has made since 1922,” he said.

What is at risk in Wyoming

Brown said the risk is not limited to one sector. Post-1922 use includes junior irrigation components, storage developed after 1922, industrial rights and most municipal supplies tied to the basin.

For irrigators, Brown pointed to a common vulnerability: even those with early priority rights often rely on “second” water, which carries a 1945 priority date and could be exposed under curtailment scenarios. He also referenced “free river” diversions used to meet irrigation needs in sandy or loamy soils where primary direct-flow allocations may not be enough in practice. Those uses, he emphasized, are not protected like a perfected right.

Municipal and industrial uses are also largely post-compact. Brown cited municipal reliance across the basin — from Pinedale to Rock Springs and Green River — alongside industrial uses such as trona operations and power generation.

“Every single one of our industrial rights… almost all of our municipal use in the basin… all of those are junior,” Brown said.

A voluntary conservation framework to keep options in Wyoming’s hands

Brown said Wyoming’s proposed legislation is designed to show “skin in the game” as the states negotiate new operating rules, while creating tools that fit Wyoming water law and reduce the likelihood of a court-driven outcome.

“The reason we’re doing it is to bring something to the table,” Brown said. “We’re willing to be part of the solution so that we can avoid litigation.”

A central obstacle, he said, is Wyoming’s “use it or lose it” structure. Beneficial use is “the basis, the measure and the limit of the right,” meaning extended non-use can trigger abandonment concerns. The bill would create a pathway for temporary, compensated conservation without risking abandonment, while requiring conserved water to return to its underlying long-term use.

“These are… short-term voluntary projects that require that water ultimately go back to the underlying use, irrigation primarily,” Brown said, noting irrigated agriculture accounts for about 84 percent of consumptive use in Wyoming’s portion of the basin.

How the program would work

Brown said the bill is Colorado River-specific because the compact apportions consumptive use rather than simply dividing river flows, changing how conservation must be measured and managed.

Applications could be submitted by water right owners or, in some cases, lessees. A typical proposal might involve temporarily not irrigating a field to reduce consumptive use, with satellite-based remote sensing used to help quantify savings.

The bill includes an injury analysis requirement consistent with Wyoming water law. It also allows consideration of broader local impacts that may not qualify as a legal injury to a water right but matter to communities, including potential effects on shallow groundwater, riparian areas and recreation.

To reduce prolonged, concentrated impacts, Brown said the bill includes participation limits. A participant could enroll for up to five years, then must return the water to its original use for a period of time before becoming eligible again.

The proposal includes abandonment protections, notice requirements and an appeal pathway through the Board of Control and the courts.

Storage and “banking” conserved consumptive use

Brown highlighted the ability to store conserved water in Fontenelle Reservoir as a key feature. Fontenelle is a federal facility with a post-compact priority date. The concept functions like a water bank, Brown said, and it could provide water supply certainty for year-round users who struggle with timing under existing tools such as temporary water use agreements and exchanges.

“Allowing this water to be stored… gives them the water certainty they’re looking for,” Brown said, adding it could reduce pressure for junior users to purchase irrigated land and permanently dry it up as a compliance strategy.

Brown said the program anticipates compensated conservation, but not funded by the State of Wyoming. Instead, compensation could come through federal grants or negotiated arrangements among water users as part of broader basin solutions.

Preparing for what comes next

Brown said Wyoming is also tracking other water-related measures, including House Bill 90, a consumptive use study; House Bill 116, addressing whether destruction of water is beneficial use; and Senate File 50, focused on groundwater study in the Laramie County control area. He also said the state is seeking funding to prepare for potential litigation, “primarily in the Colorado River Basin,” while monitoring pressure from downstream states in other basins.

The takeaway, Brown said, is Wyoming cannot afford to wait for a courtroom to dictate outcomes in a system already defined by shrinking supply.

“We need to have rules in place that deal with the hydrology that we’re actually seeing,” Brown said.

For farmers and ranchers and communities in the Green River and Little Snake basins, Brown said the intent of the voluntary conservation bill is not to concede Wyoming’s position, but to build workable tools that protect long-term agriculture, reduce the likelihood of permanent dry-up and keep Wyoming engaged as decisions are made for the West’s most contested river.

“This is a starting point,” Brown said. “We fully anticipate to learn things and make it better as it moves forward.”