Arizona announced Friday, Oct. 16, 2026, that it will join Nevada’s federal lawsuit challenging the U.S. Bureau of Reclamation’s 10-year Colorado River management plan, filing a motion to intervene in U.S. District Court. State water officials said the mandatory cuts under the plan “would devastate Arizona’s economy,” according to Department of Water Resources Director Tom Buschatzke.
Arizona filed its motion to intervene in the U.S. District Court for the District of Nevada, where Nevada launched the first state lawsuit over the river’s future on Aug. 24, 2026, according to the Arizona Department of Water Resources. Gov. Katie Hobbs’ administration pursued the intervention after the state had repeatedly threatened litigation, calling it the “nuclear option” and a last resort, officials said.
Arizona depends on the river for 36% of its water, and its supply could be cut by more than 65% under the plan, according to state officials.
The lawsuit challenges the U.S. Bureau of Reclamation’s 10-year management plan for Lakes Mead and Powell, finalized by the Department of the Interior on or about Aug. 21, three days before Nevada sued. The plan, which took effect Oct. 1, requires Arizona, Nevada and California to cut water use by up to 3 million acre-feet per year if conditions worsen, while imposing no mandatory reductions on the four Upper Basin states of Colorado, Utah, Wyoming and New Mexico, according to the federal operating framework. Reductions to Arizona’s deliveries are scheduled to begin Jan. 1, 2027.
Buschatzke said the mandatory cuts “would devastate Arizona’s economy” and “could effectively dry up the Central Arizona Project,” the 336-mile canal system that delivers Colorado River water to communities, farms and tribal water users across central and southern Arizona, including Phoenix and Tucson. Arizona faces especially large cutbacks because the CAP holds low-priority water rights, putting it among the first in line for cuts, records show.
The plan could require the three downstream states to cut as much as 40% of what they receive between 2029 and 2036, according to the Bureau of Reclamation.
Nevada Gov. Joe Lombardo said Arizona’s decision to join the lawsuit “is an important step in challenging a federal plan that unfairly burdens the Lower Basin and fails to require the Upper Basin to make meaningful reductions.” Lombardo has said the plan could cost southern Nevada more than 70% of its Colorado River allocation while requiring “not a drop” from the Upper Basin, according to his office.
Nevada’s 300,000 acre-foot allocation could be cut by up to 213,556 acre-feet in the basin’s driest years, leaving Las Vegas and surrounding cities with less than 86,500 acre-feet per year, compared with nearly 212,500 acre-feet used in 2024, according to the Southern Nevada Water Authority. Lombardo said the cuts threaten a community representing about two-thirds of Nevada’s citizens and the “lion’s share” of its economy. Federal officials did not analyze the impact on southern Nevada’s $180 billion economy, despite a legal requirement to do so, the lawsuit states. SNWA General Manager John Entsminger called the proposed shortage levels “entirely unrealistic” and said Arizona’s decision reflects “a shared commitment to ensure decisions affecting the Colorado River are based on a transparent, scientific, and legally sound process.”
Gary Wockner, executive director of Save the Colorado, voiced support for Nevada’s lawsuit, praising Las Vegas’ conservation record. Colorado’s negotiating team declined to comment on the litigation, saying they were still reviewing the filing, according to officials.
Even as they sue, Arizona, Nevada and California agreed with the federal government on cuts for the next two years, reducing water use by 3.2 million acre-feet between now and the end of 2028. Under that two-year deal, California will cut its Colorado River use by about 12%, Arizona by about 31% and Nevada by about 28%, according to the agreement. Buschatzke said Arizona is “strongly committed” to the deal and is in talks to finalize details, and the lawsuit does not target the two-year agreement, officials said.
The Colorado River provides water for about 35 million people, 30 Native tribes and roughly 5 million acres of farmland, with about three-fourths of the water going to agriculture, according to federal data. The legal fight could end up before the U.S. Supreme Court and further complicate seven-state negotiations, which deadlocked between the three downstream and four upstream states, according to water officials. The current management rules for the river expire at the end of 2026, with the new plan governing post-2026 operations.
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