Arizona has filed a motion to intervene in Nevada’s lawsuit challenging the federal government’s Colorado River operating framework, arguing that the plan could impose significant water supply reductions on Lower Basin states.

The Arizona Department of Water Resources announced the Oct. 16 filing, which seeks to protect the state’s water allocation and challenge provisions of the federal government’s Record of Decision governing river operations. Nevada filed its lawsuit in August against the U.S. Department of the Interior.

Arizona officials contend the federal framework does not adequately account for water deliveries to Lake Mead and could expose the Lower Basin states — Arizona, California and Nevada — to additional reductions beyond those contemplated in their proposed Lower Basin Agreement. Arizona Department of Water Resources Director Tom Buschatzke said the framework’s longer-term provisions could require cuts of up to 3 million acre-feet annually if specified conditions are triggered.

The dispute centers on how shortages will be shared as the states negotiate post-2026 Colorado River operations. Arizona has said it remains committed to working with California and Nevada on an agreement to conserve water over the next two years and establish a framework for managing supplies.

The Central Arizona Project, a major canal system that delivers Colorado River water to central and southern Arizona, is among the infrastructure potentially affected by deeper reductions. Arizona says joining the lawsuit will allow the state to defend its interests in court while continuing negotiations with its Lower Basin partners and the federal government.