Water & Environment · Valley-wide
Arizona joins Nevada's federal lawsuit challenging new Colorado River cuts that could shrink Southern Nevada's river supply
Arizona has intervened in Nevada's lawsuit against the Interior Department over new Colorado River rules that Nevada says could cut up to 71% of its Colorado River water supply.
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What happened
Arizona is now part of Nevada's legal fight with the federal government over how Colorado River shortages are shared. Arizona Gov. Katie Hobbs and the Arizona Department of Water Resources announced Friday that the state has intervened in the lawsuit Nevada filed in August against the U.S. Department of the Interior, The Nevada Independent reported. KTNV also reported the announcement.
The case targets a federal operating plan finalized in August. According to KTNV, it requires Nevada, Arizona and California to reduce their water use while setting no mandatory reductions for the Upper Basin states of Colorado, Utah, Wyoming and New Mexico. The framework took effect October 1.
Why the states are suing
Nevada's case
Nevada, the Colorado River Commission of Nevada and the Southern Nevada Water Authority filed suit Aug. 24, after Interior released its final plan Aug. 21, The Nevada Independent reported. Nevada was the first state to challenge that plan. KTNV reported that the suit challenges the process used to develop the new operating guidelines, and Southern Nevada Water Authority General Manager John Entsminger said Arizona shares Nevada's concerns about flaws in the federal environmental review.
Arizona's argument
Arizona officials said the federal plan fails to hold the Upper Basin accountable for delivering water to Lake Mead and could lead to Lower Basin cuts of up to 3 million acre-feet a year, according to The Nevada Independent. The state plans to challenge parts of the final environmental review and the plan itself, which it argues unlawfully fails to require releases from Upper Basin reservoirs. "We are drawing a line in the sand," Hobbs said in a statement, as quoted by The Nevada Independent.
Tom Buschatzke, the department's director and Arizona's lead Colorado River negotiator, said intervening was needed to protect the state's legal rights while keeping a negotiated outcome on the table. Arizona officials said the Central Arizona Project, which serves Phoenix and Tucson, holds relatively junior water rights and could see its river allocation cut by 77 percent over the next two years without a Lower Basin agreement.
The Upper Basin's position
KTNV reported that the Upper Basin states maintain they already use less water when river flows decline and that their legal obligations differ from those of downstream states. Utah's House speaker criticized Nevada's suit shortly after it was filed, saying it made a difficult situation harder, The Nevada Independent reported.
What it could mean for Southern Nevada
Under the federal framework, Nevada's 300,000 acre-foot allocation could be cut by as much as 213,556 acre-feet, or about 71 percent, if Lower Basin shortages reach the framework's outer limit, The Nevada Independent reported. That would leave Southern Nevada with less than 86,500 acre-feet a year. The region used about 198,000 acre-feet in 2025, according to the water authority.
KTNV reported that the lawsuit says the rules threaten the water security of more than 2.3 million residents in the Las Vegas valley. Nevada has cut its Colorado River consumption by more than 40% since 2002 even as the valley's population grew by 875,000 people, according to KTNV. In a statement Friday, Gov. Joe Lombardo called Arizona's move "an important step in challenging a federal plan that unfairly burdens the Lower Basin," both outlets reported.
The short-term Lower Basin deal
In May, the three Lower Basin states proposed an agreement committing to conserve more than 3.2 million acre-feet through 2028. Interior adopted that near-term split for 2027 and 2028, under which Arizona must cut 760,000 acre-feet a year, California 440,000 and Nevada 50,000, The Nevada Independent reported. Readers can find more on Nevada's share of that cut and earlier coverage of Arizona's plan to intervene.
Hobbs said Arizona would keep working with Nevada and California to carry out their two-year agreement while the case moves through court. Entsminger said the water authority is still working with both states to finalize it. KTNV reported that deeper cuts remain possible in later years under the federal government's 10-year framework. More water coverage is on our water page.
What to watch next
- How the lawsuit, now including Arizona, moves through federal court.
- Whether Nevada, Arizona and California finalize their Lower Basin agreement to reduce near-term demands on Lake Mead.
- Arizona's planned challenges to the federal environmental review and the final plan.
- Reductions to Arizona's water deliveries, which KTNV reported are scheduled to begin January 1, 2027.
