Water & Environment · Nevada
Arizona joins Nevada's lawsuit against federal Colorado River rules, warning of Lower Basin cuts up to 3 million acre-feet
Arizona has intervened in the lawsuit Nevada filed in August against the Interior Department's Colorado River plan, which could cut Nevada's 300,000 acre-foot allocation by nearly 71 percent under its maximum reductions.
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What happened
Arizona has joined Nevada's legal challenge to the new federal rules for the Colorado River, The Nevada Independent reported. Arizona Gov. Katie Hobbs, a Democrat, and the Arizona Department of Water Resources announced Friday that the state had intervened in the lawsuit Nevada filed in August against the U.S. Department of the Interior.
Nevada, the Colorado River Commission of Nevada and the Southern Nevada Water Authority filed the suit on August 24. According to The Nevada Independent, that made Nevada the first state to challenge the Interior Department's final plan, which was published on August 21. The dispute centers on how mandatory cuts are divided among the seven states in the river basin.
Why Arizona says it is joining
Upper Basin deliveries to Lake Mead
Arizona officials said the federal plan does not adequately require the Upper Basin states of Colorado, Utah, Wyoming and New Mexico to deliver the water they owe to Lake Mead. They said that could lead to cuts of up to 3 million acre-feet a year for the Lower Basin states. Arizona said it plans to challenge parts of the federal government's final environmental review and the final plan itself, which it argues unlawfully fails to require releases from Upper Basin reservoirs into Lake Mead.
Central Arizona Project's newer water rights
Arizona officials said the stakes are especially high for their state because the Central Arizona Project, which moves river water to Phoenix and Tucson, holds more recent water rights. Without the Lower Basin agreement, they said, the project's Colorado River share could drop 77 percent over the next two years. 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 deal with California and Nevada possible.
What is at stake for Nevada
How deep the cut could go
Under the federal framework, Nevada's 300,000 acre-foot allocation could be reduced by as much as 213,556 acre-feet, or nearly 71 percent, if Lower Basin reductions reach the framework's maximum, The Nevada Independent reported. That would leave southern Nevada with less than 86,500 acre-feet a year. Southern Nevada used about 198,000 acre-feet in 2025, according to the water authority.
An acre-foot is about 326,000 gallons. The outlet described that as enough to cover a football field with a foot of water or to supply two to three homes for a year.
The short-term Lower Basin deal
In May, Arizona, California and Nevada proposed a Lower Basin agreement that would conserve more than 3.2 million acre-feet through 2028. The Interior Department adopted that split of short-term cuts for 2027 and 2028. Under it, Arizona must cut its use by 760,000 acre-feet a year, California by 440,000 and Nevada by 50,000. More on Nevada's 50,000 acre-foot short-term cut is in our earlier coverage.
How officials reacted
Hobbs said in a statement that Arizona is drawing a line. She added that the state will keep working with Nevada and California to carry out their own two-year Lower Basin agreement while the case moves through the courts.
Nevada Gov. Joe Lombardo, a Republican, said in a statement Friday that Arizona's move is an important step in challenging a federal plan he said unfairly burdens the Lower Basin. He said Nevada remains committed to a negotiated solution but will not accept a framework that puts the state's water supply at risk.
Southern Nevada Water Authority General Manager John Entsminger said Arizona shares Nevada's concerns about flaws in the federal environmental review and in the process used to develop the post-2026 framework. He said the agency continues to work with California and Arizona to finalize the Lower Basin agreement. The speaker of the Utah House criticized the lawsuit shortly after it was filed, saying it made a difficult situation harder, the outlet reported. Follow more regional coverage in our water section.
What to watch next
- Arizona's planned challenge to parts of the federal final environmental review and the final Colorado River plan.
- Efforts by Arizona, California and Nevada to finalize their two-year Lower Basin agreement to reduce short-term demand on Lake Mead.
- How Nevada's lawsuit against the Interior Department proceeds in court now that Arizona has intervened.
