Arizona asks to join Colorado River lawsuit over cuts

Arizona filed a motion Friday seeking to join Nevada’s federal lawsuit over post-2026 Colorado River operating rules, a case that could shape how deeply the Central Arizona Project is cut after the current two-year shortage plan.

The Oct. 16 filing in U.S. District Court in Nevada asks to add Arizona as an intervenor in case 2:26-cv-02665-GMN-NJK. The attached complaint seeks declaratory and injunctive relief against the U.S. Department of the Interior and Bureau of Reclamation.

Arizona’s move does not by itself stop the federal rules, change city water deliveries or mean the state has won any claim. The court must first decide whether Arizona may intervene, and the underlying case remains pending.

Why the case matters in the West Valley

Colorado River water reaches Maricopa County through the Central Arizona Project, making the dispute relevant to West Valley cities even though the lawsuit was filed in Nevada.

Local planning already shows how statewide allocation changes translate into city-level numbers. Avondale’s 5,416-acre-foot annual CAP subcontract is expected to lose 758 acre-feet in both 2027 and 2028 under a projected 14% reduction to the municipal-and-industrial pool. The city is scheduled to consider a firming agreement Oct. 19 that would provide ways to use stored-water credits as a backup.

Glendale has also identified stored credits, wells and other supplies in its shortage response. Those preparations remain in place. Friday’s legal filing does not cancel the scheduled 2027 and 2028 reductions.

The longer-term risk is the amount and distribution of cuts later in the decade. Arizona says the federal framework could allow Lower Basin reductions of as much as 3 million acre-feet per year, depending on river conditions and later decisions. A reduction of that scale would place much greater pressure on CAP deliveries than the two-year plan now being used by cities for budgeting and supply planning.

What Arizona is challenging

The Interior Department approved its latest operating framework Aug. 21 after the seven Colorado River Basin states failed to reach a broader agreement. The plan calls for Arizona, California and Nevada to reduce Lower Basin deliveries by 1.25 million acre-feet in each of 2027 and 2028. Arizona’s share is 760,000 acre-feet a year.

Arizona is seeking to preserve that two-year Lower Basin arrangement while challenging parts of the federal decision that govern the years that follow. In an Oct. 16 announcement, Gov. Katie Hobbs and the Arizona Department of Water Resources said the state wants the federal government to enforce what Arizona considers Upper Basin delivery obligations to Lake Mead.

The state’s motion to intervene argues that the federal actions could directly affect Arizona’s water for the next decade and its rights under the Colorado River Compact. Those are Arizona’s legal claims. The federal government will have an opportunity to respond, and the court has not ruled on their merits.

Nevada filed the original lawsuit in August, alleging the federal government violated administrative and environmental law when it adopted the new framework. Arizona’s filing would let the state present its own claims in the same case instead of relying on Nevada to represent Arizona’s distinct water interests.

What happens next

The immediate milestone is a court ruling on Arizona’s intervention request. No hearing date or decision deadline was identified in the state’s announcement.

For West Valley residents, the practical near-term picture is unchanged: cities continue preparing for the 2027 and 2028 CAP reductions through stored-water credits, wells and diversified supplies. The lawsuit is aimed at the federal rules behind those cuts and the possibility of substantially deeper reductions later.

Featured image: AI-generated editorial illustration representing Colorado River litigation and Central Arizona Project water policy. It does not depict a specific site, court proceeding or official plan.