- Arizona has joined Nevada in challenging federal Colorado River water rules.
- An Arizona State University law professor questioned the timing of Arizona’s decision.
- Both states challenge the federal government’s legal and environmental reviews.
- Arizona wants to preserve a short-term water plan that Nevada wants overturned.
- The lawsuit could complicate ongoing negotiations among Colorado River states.
Wednesday, October 21, 2026 — Arizona’s decision to join Nevada’s lawsuit against the federal government was not unexpected, but the timing surprised one legal expert.
In an October 19, 2026, interview with KJZZ’s Mark Brodie, Arizona State University law professor Rhett Larson said he expected Arizona to become involved eventually. However, he thought the state might wait until the federal government responded to Nevada’s original lawsuit, filed in August.
“I’m not surprised that Arizona got involved. I’m a little surprised they got involved at this stage,” Larson told KJZZ
.
The lawsuit challenges federal rules governing Colorado River water allocations. Under those rules, Arizona, Nevada and California face water reductions through 2028, while the four Upper Basin states would not be required to make cuts.
Arizona and Nevada Want Different Outcomes.
Although both states argue that federal officials violated legal procedures, environmental review requirements, and Colorado River law, they disagree about which rules should be overturned.
According to Larson’s KJZZ interview, Nevada wants the court to throw out both the next two-year water plan and a longer 10-year framework.
Arizona also wants the 10-year framework overturned but wants to keep the two-year plan.
Larson explained that Arizona favors keeping the shorter plan because it provides greater certainty while Arizona, California and Nevada continue negotiating water reductions.
Could the Lawsuit Complicate Negotiations?
Larson told KJZZ that disagreements between parties in the same lawsuit are not unusual. However, Arizona’s position complicates matters because it challenges the federal government’s analysis while supporting part of the resulting plan.
He also warned that a court victory could lead to an appeal, adding more uncertainty.
Larson suggested the lawsuit might encourage renewed negotiations, although he expressed little optimism about that outcome.
He also raised the possibility of future litigation between Upper and Lower Basin states, which could bring the dispute directly before the U.S. Supreme Court.
