The lawsuit could take years to resolve and may eventually reach the U.S. Supreme Court, although no court date has been set. The Department of the Interior and the Bureau of Reclamation have until the end of October 2026 to formally respond to Nevada’s initial complaint.

Interior Secretary Doug Burgum warned that taking the dispute to court could hurt Arizona, which already faces substantial reductions in its river supply. “The last thing that Arizona should want to do is have a judge decide where the water is going to go,” he said during a visit to southern Arizona earlier this week.

Democratic U.S. Rep. Greg Stanton defended the state’s decision to join the challenge, calling it a necessary step to protect Arizona’s long-term water supply. He said the current federal plan cuts Arizona’s allocation by about 30% for the next two years, but argued the larger concern is whether additional reductions will follow.

Stanton contends that Lower Basin states — Arizona, California and Nevada — are being asked to take a disproportionate share of future cuts, while Upper Basin states face no comparable mandatory reductions under the plan. The lawsuit seeks to contest that balance, he said.

The Colorado River serves roughly 40 million people in the western United States and Mexico, supplying cities, farms and industry. Its allocation is governed by agreements, laws and court rulings developed over more than a century. Prolonged drought and declining reservoir levels have intensified pressure on that system.

Burgum questioned whether Arizona has grounds to sue, saying he believes the case could be dismissed because the state has not demonstrated an injury. He also pointed to Arizona’s comparatively junior water rights, warning that a judge’s decision on future allocations might not favor the state.

The federal government developed its plan after 20 months of talks among the seven states failed to produce an agreement, Burgum said. He added that federal officials remain willing to help negotiate a longer-term solution.

The conflict has economic stakes for Arizona as well as its cities and farms. Stanton pointed to the state’s expanding semiconductor manufacturing sector, which depends on reliable water supplies, and called water security important to national defense.

Both officials acknowledged the river’s supply challenges. Burgum cited low reservoir levels and poor snowpack, and said new technologies such as desalination could help increase available water. Stanton called for federal investment in water recycling, advanced purification and infrastructure that would allow Valley communities to reuse more wastewater.

Those projects are costly, Stanton said, and Arizona will need to reduce its dependence on the Colorado River regardless of the lawsuit’s outcome. He also argued that Upper Basin states should make reductions as the region adapts to having less water.