U.S. Bureau of Reclamation officials are considering whether to order Arizona, California and Nevada to take less water out of the drying Colorado River, effectively flexing their muscles over a problem they had hoped the states would solve themselves.

In the coming weeks, federal officials must decide whether to impose cuts on the three lower Colorado River Basin states by either following the longstanding system of water-rights seniority or by spreading them across three states evenly.

The former would put Arizona squarely in the crosshairs — threatening cities like Phoenix and Tucson — while the latter would force far more significant cuts on California, which draws the most Colorado River water by far.

Colorado and the three other upper-basin states — New Mexico, Utah and Wyoming — appear to have avoided cuts of their own, at least in the short term.

The Bureau of Reclamation’s two proposals to cut water allocations for lower-basin states are part of a supplemental environmental impact statement for the Colorado River published Tuesday. Federal officials expect to choose one this summer, and the plan would go into effect next year and guide the seven-state river basin through 2026.

The move strengthens the federal agency’s resolve to conserve water from the Colorado River as the seven states within its basin repeatedly fail to find common ground, said Rhett Larson, a water law professor at Arizona State University.

“I am reading this as a shot across the bow,” Larson said. “The federal government is saying, ‘Brace yourselves, because if you don’t come up with something, we will.’”

The cuts are needed because, despite a massive snowpack in the Rocky Mountains this winter, water levels at lakes Powell and Mead — the country’s two largest reservoirs — are still projected to diminish as they face historically dry conditions exacerbated by climate change.

“We’re thankful for this winter’s snow and rain,” Deputy Interior Secretary Tommy Beaudreau said at a news conference Tuesday.

But, he added, “One good year will not save us from more than two decades of drought.”

While federal officials consider their options, each of the seven states in the Colorado River Basin will continue to negotiate water use for the long term. At risk is the water supply for cities, towns, farms and industries across the West.

And if any of the states or Native American tribes in the basin sour on the plan they could sue, which would plunge the entire scheme into an expensive and time-consuming legal tangle.

Tuesday’s announcement kicks off a 45-day period during which the Bureau of Reclamation will accept public comments on the proposal from cities, states, tribes, utilities and more, to tweak the three options on the table.

The first option would be to take no additional action, which means conditions along the Colorado River would worsen. Water levels at lakes Powell and Mead would likely sink deeper.

This would bring on the worst effects of the ongoing drought, Reclamation Commissioner Camille Calimlim Touton said during Tuesday’s news conference.

The second option would cut water use from lower-basin states “based predominantly on the priority of water rights.”

Under the Colorado River’s prior-appropriation legal system, those that have been drawing water from the river the longest have a higher priority. So cuts would be imposed on those with the youngest water rights.

This option likely would hit Arizona the hardest, said Jennifer Gimbel, senior water policy scholar at Colorado State University. She mentioned that the Central Arizona Project, which supplies cities including Phoenix and Tucson, would be at risk of losing water.

The third option would skip the priority system in favor of evenly distributing water cuts among the lower-basin states by a flat percentage. With this approach, California, which draws the most water from the Colorado River and frequently consumes more than its allotment, also would face steep cuts.

“So we can do nothing, do what California wants or do what everybody else wants and have cuts across the board,” Larson said.

Doing nothing isn’t an option, Larson said. Doing what California wants could devastate several major cities and cutting water use equally could be illegal and result in major lawsuits.

Larson said he feels as though federal officials, particularly President Joe Biden, might ultimately learn further toward cutting water use across the board.

Aside from imposing water cuts, the second and third options would also reduce the amount of water released downstream from Lake Powell to lower-basin states. This would give reservoirs in the upper-basin states a chance to recover, Gimbel said — but it would come too late to capitalize on this year’s snowpack.