Arizona seeks to join Nevada's Colorado River lawsuit. Here's where Yuma fits.

Arizona's motion to join Nevada's Colorado River lawsuit doesn't mention Yuma once.

It talks about semiconductor plants and the Central Arizona Project's 336-mile canal. It talks about tribes, farmers and the 1922 Colorado River Compact. It runs through decades of reservoir rules in careful detail. Yuma, which sits at the bottom of the river with some of the oldest water rights in the state, never comes up.

That's not quite a snub. It reflects how this particular fight works.

What Arizona did

On Oct. 16, the State of Arizona, acting through the director of the Arizona Department of Water Resources, asked to join State of Nevada v. Burgum in federal court in Nevada (Case No. 2:26-cv-02665). Nevada, the Colorado River Commission of Nevada and the Southern Nevada Water Authority filed the suit Aug. 24 against Interior Secretary Doug Burgum, the Interior Department and the Bureau of Reclamation.

Both states are challenging the same three federal actions:

1. The Final Environmental Impact Statement on post-2026 operations of Lake Powell and Lake Mead (July 2026)
2. The Record of Decision setting a decision framework for 2027 through 2036 (August 2026)
3. The 2027-2028 Guidelines for coordinated operation of the two reservoirs (August 2026)

Arizona's core claim is that the rules break the Law of the River. In the state's reading, they let Lake Powell release far less water downstream than the 1922 Compact requires the Upper Basin to deliver. The motion counts the Upper Basin's obligation at Lee Ferry as 75 million acre-feet every 10 years, plus 7.5 million toward Mexico's share, for 82.5 million in all. Arizona says the federal preferred plan would release a median of 6 million acre-feet a year from Powell in critically dry conditions, and possibly as little as 5 million. The motion argues that would put 10-year deliveries well under what the Compact calls for.

Arizona is also making procedural arguments. It says federal agencies didn't respond to its comments on modeling, on economic effects and on the Lower Basin's own 2024 proposal, as federal environmental and administrative law require.

Where Arizona and Nevada split

Arizona isn't just signing on to everything Nevada wants. The two states want different things done about the 2027-2028 Guidelines.

Nevada wants those guidelines thrown out. Arizona wants them sent back to the agency to be fixed without being thrown out, so the next two years of river operations aren't upended. For the longer-term Environmental Impact Statement and Record of Decision, Arizona wants a court to vacate them and block enforcement.

Gov. Katie Hobbs put it bluntly: "we will not accept a forced federal plan that solves this crisis on the backs of our families, farmers, and businesses." ADWR Director Tom Buschatzke said joining the suit "is necessary at this time for Arizona to protect its legal rights to Colorado River water."

In its announcement, the state said it still wants to finish a separate two-year agreement among the Lower Basin states. Under that deal, Arizona, California and Nevada would conserve more than 3.2 million acre-feet in 2027 and 2028. The governor's office says that without it, the Central Arizona Project's Colorado River supply would be cut 77% over the next two years.

So where does Yuma fit?

Here's the part the motion skips.

Arizona's cut under the new rules is big. As we reported Oct. 8, the 2027-2028 Guidelines reduce the Lower Basin by 1.25 million acre-feet a year, and Arizona's share is 760,000 acre-feet, about 60% of the total. The motion repeats those figures.

But the cut doesn't fall evenly across Arizona. Colorado River water is divided by priority. Reclamation's records place the City of Yuma, the Wellton-Mohawk district and the Yuma Mesa division in the third priority, and some local users hold first-priority "present perfected rights." The Central Arizona Project is fourth priority. When shortages hit, junior users like CAP generally get cut before senior ones.

That's why the motion keeps coming back to CAP and the Phoenix-Tucson corridor. Most of the near-term pain lands there.

None of that guarantees Yuma comes through untouched. Senior rights are a legal position, not a force field. A Lake Mead decline deep enough could still raise questions for everyone downstream. And the City of Yuma is preparing its own legal options. In September, the City Council authorized the City Attorney to explore a challenge to the same federal decision. As of our last check, the City hadn't filed anything.

For Yuma, the outcome that matters most is whether the courts accept Arizona's argument that the Upper Basin owes more water to Lake Mead. More water in Mead means less pressure on everyone's place in line, including the senior users.

What to watch

• Whether the court grants Arizona's motion to intervene
• Whether the Lower Basin states sign their two-year agreement, and whether the Arizona Legislature approves it, as state law requires for agreements affecting Arizona's river rights
• Whether the City of Yuma, or Yuma-area irrigation districts, file their own challenges

Sources

• State of Arizona, Motion to Intervene and proposed Complaint in Intervention, Nevada v. Burgum, Oct. 16, 2026
• Office of the Arizona Governor, Oct. 16, 2026 announcement
• Nevada Governor's Office, lawsuit announcement
• Yuma Informed, new Colorado River rules, Oct. 8
• Yuma Informed, Yuma Council legal fights, Sept. 26