Arizona is officially entering the legal fray against a federal plan that could significantly curtail its water allocation from the vital Colorado River, a move underscoring the escalating tensions over dwindling water resources in the American West. The Arizona Department of Water Resources filed a motion Friday to join Nevada’s existing lawsuit, arguing that the federal government’s ten-year management strategy for the imperiled river would inflict severe economic damage on the state. "The State’s towns, cities, tribes, farmers, factories, and businesses cannot survive without sufficient water from the Colorado River," state attorneys asserted in their legal filing.

The dispute centers on a federal plan designed to address the chronic decline of the Colorado River, a critical water source for some 40 million people across seven Western states and Mexico. Nevada initiated its legal challenge in late August, contending that the federal agencies’ strategy disproportionately burdens the Lower Basin states – Arizona, Nevada, and California. The river’s diminishing flow is a stark consequence of a confluence of factors, including escalating climate change, which reduces snowpack and subsequent runoff that replenishes reservoirs like Lake Mead and Lake Powell, and historical water allocation agreements struck in the mid-20th century that promised more water than the river can now reliably provide. Faced with an inability for the seven Colorado River Basin states to reach a consensus on how to manage the crisis, the federal government stepped in with a plan intended to better align water withdrawals with the river’s declining capacity.

Both Arizona and Nevada argue they have already made substantial water conservation efforts and are being unfairly singled out for further reductions. Tom Buschatzke, Director of the Arizona Department of Water Resources, stated on October 16th, "The Lower Basin states have contributed millions of acre-feet of water toward stabilizing the river system. With more than 5.5 million acre-feet of Arizona water left in Lake Mead since 2014, no state has sacrificed more." He added, "The US decision puts the entire burden of sacrifice on the shoulders of three states. We are joining Nevada in challenging that framework."

The Colorado River’s water is divided between the Upper Basin states – Colorado, New Mexico, Utah, and Wyoming – and the Lower Basin states of Arizona, Nevada, and California. The foundational agreement governing these allocations, the 1922 Colorado River Compact, assigns 7.5 million acre-feet of water annually to each basin, with an additional smaller allocation for parts of Mexico. The individual states within each basin then further divide their allotted shares. To put these figures into perspective, one acre-foot of water is equivalent to nearly 326,000 gallons, enough to cover an acre of land one foot deep. In Arizona, this quantity typically suffices to supply three single-family homes for an entire year.

California, as the largest water user in the Lower Basin, receives the most substantial allocation of Colorado River water, amounting to 4.4 million acre-feet per year, or approximately 27% of the total. Arizona’s annual allocation is 2.8 million acre-feet (about 17%), while Nevada receives a significantly smaller share of 300,000 acre-feet (around 2%). These figures, derived from Congressional reports and analyses by public policy institutions, highlight the stark differences in water dependence among the Lower Basin states.

The U.S. Bureau of Reclamation’s plan mandates that the Lower Basin states bear the brunt of potential cuts. For Arizona, this translates to a proposed reduction of 760,000 acre-feet annually, representing roughly a quarter of its water allocation and the most significant cut among the three Lower Basin states. California would be required to reduce its usage by 440,000 acre-feet per year, and Nevada by 50,000 acre-feet, with potential total cuts reaching up to 3 million acre-feet. Notably, the federal government is not imposing mandatory cuts on the Upper Basin states, instead requesting voluntary contributions of 200,000 acre-feet each from them over two years.

Arizona Governor Katie Hobbs expressed her state’s position firmly, stating on Friday, "Arizona has always been willing to do our part to protect the Colorado River, but we will not accept a forced federal plan that solves this crisis on the backs of our families, farmers, and businesses."

The Department of the Interior, however, criticized Arizona’s legal maneuver, asserting that the federal administration is actively collaborating with Basin states, tribes, and water users to reach an agreement. A spokesperson for the Department of the Interior commented, "Governor Hobbs is wrong, and it’s unfortunate to see Arizona playing politics instead of working toward meaningful solutions. Litigation won’t create a single additional drop of water or change the hydrologic realities facing the Colorado River Basin."

In its complaint filed alongside the motion to join Nevada’s lawsuit, Arizona alleges a fundamental flaw in the federal government’s environmental review process that underpinned the decision. The state claims that every federal alternative considered "assumed that the Upper Basin States would make no meaningful reduction in their own use, no matter how little water the River produced." The complaint further elaborates, "The alternatives placed the full burden of any resulting shortfall on the Lower Basin."

Western water rights operate under a "first in time, first in right" doctrine, a system that prioritizes users who established their water claims earlier. This principle means that Arizona’s Colorado River rights are of a lower priority than those acquired earlier by California. The potential reductions outlined in the federal plan could have a devastating impact, as described by Buschatzke: "Such reductions could effectively dry up the Central Arizona Project canal system, as well as many of our on-river communities and would more than double the water cuts agreed to in the Lower Basin Agreement."

Nevada’s lawsuit, filed just three days before the U.S. Department of the Interior formally announced its Colorado River plan in August, argued that the proposed cuts "will cause devastating environmental, socioeconomic, and health and human safety impacts to southern Nevada and its citizens." The lawsuit also contends that the federal plan violates several provisions of the "Law of the River," a complex body of agreements, treaties, statutes, and court decisions that govern the management of the Colorado River.

Nevada Governor Joe Lombardo welcomed Arizona’s decision to join the litigation, stating that it represents "an important step in challenging a federal plan that unfairly burdens the Lower Basin and fails to require the Upper Basin to make meaningful reductions." Arizona officials believe that by intervening in Nevada’s existing lawsuit, they can avoid the complexities and costs of initiating a separate, parallel legal action and effectively represent the state’s interests within the ongoing legal proceedings. "Arizona believes that taking this action now provides the best path forward for protecting Arizona water users," Buschatzke concluded.