Lake Mead has dropped to its lowest level since the reservoir was filled nearly 90 years ago, raising the prospect of deeper Colorado River cuts for Arizona cities, farms and tribes.

The reservoir stood at 1,040.4 feet above sea level on Aug. 7, edging below the previous record set in July 2022, according to federal data reported by The Associated Press. The new low followed the Colorado River Basin’s driest winter on record and came after the seven states that rely on the river failed to reach an agreement.

Under a proposed Bureau of Reclamation framework, Arizona, California and Nevada could be required to cut their combined use by as much as 3 million acre-feet a year through 2036. The reductions would be recalculated every two years based on river flows and reservoir levels.

Arizona is especially vulnerable because much of the water it receives through the Central Arizona Project has lower legal priority than California’s major agricultural and urban entitlements. The 336-mile CAP canal serves Maricopa, Pinal and Pima counties, home to nearly 80% of the state’s population.

Arizona is already taking a 512,000-acre-foot reduction this year under a Tier 1 shortage declaration. Most of that cut has fallen on farms and other lower-priority users. Deeper reductions could reach cities, tribal communities and industrial users.

In a short-term plan developed by the Lower Basin states, Arizona offered to conserve 760,000 acre-feet a year in 2027 and 2028. California proposed saving 440,000 acre-feet, and Nevada 50,000 acre-feet.

State officials estimated the plan could reduce CAP deliveries to cities by about 14% and tribal supplies by about 10%. Those cuts could grow if Lake Mead and Lake Powell continue to fall.

In an April 16 meeting with U.S. Department of the Interior Assistant Secretary Andrea Travnicek and Bureau of Reclamation Acting Commissioner Scott Cameron, Senate President Warren Petersen and House Speaker Steve Montenegro led Arizona Republican legislative leaders in pressing for measures beyond the Lower Basin plan.

They asked the federal government to release water from Upper Basin reservoirs under the 1956 Colorado River Storage Project Act, arguing the releases would protect hydropower at Lake Powell and keep the reservoir from reaching dead pool, the point at which water can no longer flow through the dam.

Their proposal pairs $1 billion a year for voluntary conservation with federal support for storage, groundwater recharge, reuse and desalination projects.

State Sen. Tim Dunn, a Yuma Republican who attended the federal meeting, has warned that the Lower Basin plan may not conserve enough. Dunn is vice chairman of the Senate Natural Resources, Energy and Water Committee.

“If next year’s hydrology is as bad as this year, we need a 2.5 million acre-feet a year cut,” Dunn said in July.

Dunn represents some of the country’s most productive farmland. Yuma-area growers hold stronger river rights than many CAP users and supply much of North America’s winter produce. Even so, severe reductions could push senior agricultural users to conserve water or leave fields unplanted.

On one point, Arizona’s leaders agree across party lines: the state should not shoulder the burden alone.

Congressman Andy Biggs, the Republican nominee for governor, led Arizona’s GOP congressional delegation in opposing earlier versions of the federal framework.

“We cannot accept a framework that punishes responsible stewardship while ignoring long-standing legal obligations under the Compact and the Law of the River,” Biggs said.

Democratic Gov. Katie Hobbs has made a similar case. She says Arizona, California and Nevada have offered measurable reductions while Colorado, New Mexico, Utah and Wyoming have resisted mandatory cuts.

Upper Basin officials respond that drought and reduced snowfall already constrain their water use and that mandatory reductions could violate the 1922 Colorado River Compact.

Phoenix gets about 40% of its water from the Colorado River, with most of the rest coming from the Salt and Verde rivers. Tucson has substantial reserves and uses less than its full CAP entitlement.

Those reserves make immediate residential shortages unlikely, but higher costs could arrive sooner. Cities may have to pump and treat more groundwater, expand wastewater reuse, buy higher-priority water or build new infrastructure.

“We are not running out of water,” Arizona State University water law professor Rhett Larson told The Associated Press. “We’re running out of cheap water.”

The stakes go beyond household water bills. CAP water supports tribal economies, semiconductor manufacturing, construction, power generation and agriculture. Reduced supplies could also make it harder for growing communities to demonstrate the 100-year water supply required for new subdivisions.

Biggs and U.S. Rep. Greg Stanton, a Democrat, have jointly sought at least $500 million in remaining federal drought-mitigation funds. The money could pay farmers, tribes and cities to leave water in Lake Mead, but temporary conservation does not solve the river’s central problem: It produces less water than states, tribes and Mexico were promised.

Arizona officials must now decide whether to accept steep negotiated cuts, challenge the federal plan in court or risk harsher reductions if the reservoirs keep falling.