The federal government on Tuesday laid out two options for preventing the Colorado River’s depleted reservoirs from falling to critically low levels, saying water cuts could be imposed across the Southwest by following the water rights priority system or by using an across-the-board percentage.

The stakes in the decision are high for California, which receives the largest share of water from the Colorado River, as well as for Arizona and Nevada. Imposing an equal across-the-board cut would hit California harder, particularly in agricultural regions, while strict adherence to the water rights priority system would bring larger reductions for cities such as Phoenix and Las Vegas.

The U.S. Bureau of Reclamation presented its alternatives as an initial step in a review aimed at revising the rules for dealing with shortages through 2026. Federal officials said that the proposals still could change and that a solution somewhere between the two options could emerge as representatives of states, water agencies and tribes continue negotiations on how to address the chronic water shortages.

“The prolonged drought afflicting the American West is one of the most significant challenges facing our country today,” Deputy Interior Secretary Tommy Beaudreau said.

Beaudreau spoke beside other officials in a room overlooking Hoover Dam and Lake Mead, where the reservoir now stands at 28% of capacity, its surface lapping about 180 feet below the high-water mark along its rocky shores.

The river’s reservoir levels have declined dramatically during 23 years of drought intensified by climate change. Even after storms that have blanketed the Rocky Mountains with the largest snowpack since 1997, federal officials say the likelihood of a return to dry conditions means the region still needs a plan for apportioning additional water cuts if necessary over the next three years.

“Everybody understands the significance of the crisis,” Beaudreau said. “I think everybody understands that, as fortunate and thankful we are for the precipitation, that nobody’s off the hook, and that there needs to continue to be unity in trying to develop solutions.”

Representatives of seven states, water agencies and tribes have been discussing options for reducing water use to prevent the reservoirs from dropping toward dangerously low levels.

The Bureau of Reclamation said it released its initial review of alternatives, called a draft supplemental environmental impact statement, to “address the continued potential for low run-off conditions and unprecedented water shortages” in the Colorado River Basin. Officials said they need plans in place to protect critical levels at Lake Mead and Lake Powell and prevent them from dropping so low that the dams would stop generating power and water deliveries would be at risk.

The agency is revising the 2007 guidelines for its operations of Glen Canyon Dam and Hoover Dam, which include measures for dealing with shortages through 2026 — but which federal officials say would no longer be sufficient if reservoirs continue to decline.

The Biden administration released its options more than two months after officials from California and six other states presented two conflicting proposals for water reductions.

Closed-door talks among state officials and managers of water agencies are set to continue while the federal government receives input on the proposals. And representatives of California, Arizona and other states pledged to continue working toward a seven-state consensus.

Under one of the options, the federal government would consider making water reductions based predominantly on the existing priority system for water rights.

That would mean smaller cuts or no cuts for agencies and entities that hold older senior rights, including agricultural suppliers such as California’s Imperial Irrigation District, which uses the single largest share of Colorado River water to supply about 500,000 acres of farmland in the Imperial Valley. Strict adherence to the water rights priority system would also mean large cuts for junior water rights holders that started taking water from the river later, such as the Central Arizona Project, which supplies Phoenix, Tucson and other cities.

Under the second alternative, the Bureau of Reclamation would analyze the effects of reductions “distributed in the same percentage” for all water users in the three Lower Basin states of California, Arizona and Nevada.

This approach would mean across-the-board cuts for all water users in the region, including senior water rights holders, amounting to a reduction of about 13% on top of cuts that were already agreed to under a 2019 deal. Agricultural irrigation districts, cities and tribes would all need to participate based on a schedule of reductions tied to the levels of Lake Mead.

Beaudreau said this second alternative reflects the Interior secretary’s authority to “provide for human health and safety” and manage supplies under emergency conditions.

Both of the alternatives call for progressively larger reductions as the level of Lake Mead declines. The total amount of potential cuts in 2024, including reductions under existing agreements, could reach slightly more than 2 million acre-feet — a major reduction from the three states’ total apportionment of 7.5 million acre-feet.

Last year, federal officials called for cutting water use by 2 million to 4 million acre-feet per year to address unresolved water shortfall and the effects of climate change.

The federal review will also look at a “no action alternative,” analyzing the consequences of staying with the existing rules and agreements if dry conditions return after this year’s wet winter.

“One good year will not save us for more than two decades of drought,” Beaudreau said.

The heavy snow this winter, he said, may push “the curve out six months or more.”

“But the trend is still evident over this time period and evident in the modeling,” Beaudreau said. “The downward trajectory of this system has worsened. We cannot kick the can on finding solutions.”

The Bureau of Reclamation will accept public comments on the draft proposals until May 30, and Beaudreau said the agency expects input from states, tribes and water agencies on “fine-tuning or adjusting those alternatives.”

The government plans to adopt a final decision this summer, which will guide dam operations and water releases in the coming year.

The options presented by the Bureau of Reclamation show the sorts of cuts that could be imposed if the region doesn’t reach an agreement, said Adel Hagekhalil, general manager of the Metropolitan Water District of Southern California, which supplies Colorado River water across the region.

“Neither of the action alternatives presented today is ideal,” Hagekhalil said. He said that both “include significant supply cuts that would hurt Metropolitan and our partners,” and that the region should find a better way to manage the river.

“We must keep working to develop a consensus short-term plan, while also collaborating to build long-term solutions that will ensure the river’s lasting sustainability,” Hagekhalil said.

The proposals should provide bookends to help in the talks among the states, tribes and water agencies, Beaudreau said.

Estevan López, New Mexico’s representative, said the draft proposals provide a “framework on which we can build, and perhaps find something that is partway between those two bookends.”

The option of cuts based on an across-the-board percentage represents the worst-case scenario for California, said Elizabeth Koebele, an associate professor of political science at University of Nevada, Reno.

By laying out this scenario, Koebele said, the Interior Department is “signaling that they are willing to impose these deep cuts on California, and that California must negotiate with the other six basin states if it wants a better water deal, which is a powerful motivator.”

In addition to settling on an approach for the next three years, managers of water agencies still need to negotiate new rules for dealing with shortages after 2026.

Whatever option the federal government decides to choose, much will depend on reservoir levels over the next three years.

In the Rocky Mountains, the snowpack in the Upper Colorado River Basin now measures 156% of the average since 1991, making it one of the largest since 1980.

The runoff this spring and summer will boost the level of Lake Powell on the Utah-Arizona border, and the water will make its way to Lake Mead, which stores supplies for Southern California, Arizona, southern Nevada and northern Mexico.

But Lake Powell and Lake Mead are still expected to remain well below half-full.

“Unprecedented conditions require new solutions,” Bureau of Reclamation Commissioner Camille Calimlim Touton said. “To meet this moment, we must work together through our shared values and a commitment to protecting the river.”