On the outskirts of Phoenix, a small desert town that depends heavily on the Colorado River has capped its growth, brought old wells back into service, and negotiated water deals. Even so, Cave Creek Mayor Robert Morris cannot dismiss the very real possibility that these measures will not be enough to sustain the community of roughly 5,000 people well into the future — and a recent federal plan aimed at easing a deepening crisis in the river basin will not help.

Cave Creek draws nearly all of its water from the Colorado River, which supplies 40 million people across the U.S. West and has been shrinking under the combined pressures of climate change, demand, and overuse. The river's allocations were apportioned among the basin's states under the 1922 Colorado River Compact and a web of subsequent agreements, court decrees, and treaties — a framework built on early-20th-century flow assumptions that today's shrinking river no longer meets. The town was already forced to make cuts this year and stands to lose more under the new federal plan.

Morris likened the situation to planning for a meteor strike.

"You can see it coming, but you can't get out of the way and you don't know what the damage is going to be," he said.

The uncertainty extends across seven U.S. states, tribal nations, and Mexico. Farmers are weighing which crops justify the investment. Phoenix could lose a portion of its municipal and industrial water for the first time and be forced to turn to backup supplies. Residents, in turn, could face even more expensive water.

Nevada raised the stakes this week by suing the Interior Department and the U.S. Bureau of Reclamation, arguing that basic needs in the Las Vegas region will go unmet if the area must absorb planned reductions of up to 70% of its Colorado River water over the next decade. The bureau said Thursday that it does not comment on litigation. The lawsuit signals that the legal battles over how shortages are shared — long confined mostly to negotiations among states, tribes, and the federal government — are now moving into the courts.

"The uncertainty is going to continue to build in the wrong direction," said Tom Buschatzke, director of the Arizona Department of Water Resources.

In the U.S. West, water is stored primarily in reservoirs, aquifers, and snowpacks. But a record snow drought means there is far less water available to recharge those sources.

The country's two largest reservoirs — Lake Mead and Lake Powell — serve as barometers of the Colorado River system's health, and both hit record lows this month. Eight other reservoirs operated by the Bureau of Reclamation have recently recorded their lowest levels in at least 30 years. They include Elephant Butte Lake in New Mexico, which is critical for supplying water for crops in southern New Mexico, Texas, and Mexico; the Green Mountain Reservoir, which serves western Colorado; and Wyoming's Guernsey Reservoir, which funnels water to farmers in eastern Wyoming and western Nebraska.

Under the Bureau of Reclamation's plan, California, Nevada, and Arizona will collectively cut water use by 1.25 million acre-feet (about 1.54 billion cubic meters) — enough to fill more than 600,000 Olympic-sized swimming pools — annually over the next two years, with the possibility of larger reductions depending on conditions. Colorado, Utah, Wyoming, and New Mexico are not required to make cuts for now, though they could voluntarily reduce water use.

While El Niño could bring intense moisture to the northern Rockies and the Southwest in the coming months, it will not erase decades of drought.

"Drought is a slow-moving phenomena and it can take some time to come into it and also come out of it," said David Mocko, a senior research scientist who authored a recent U.S. Drought Monitor map.

In Yuma, Arizona — a region that produces about 90% of the leafy greens eaten in North America during the winter — John Boelts grows vegetables, melons, durum wheat, and other crops. Farmers there hold high-priority rights and may avoid cuts to their Colorado River supply over the next two years, but Boelts said the reprieve is not enough to support longer-term planning, making farmers reluctant to plant new acreage. Orchard crops that thrive in the region, such as citrus and dates, take years to become commercially productive, he noted. That hesitancy in the fields reaches beyond the basin: winter salad greens and vegetables shipped nationwide trace back to Colorado River water, meaning shortages here can ripple into grocery supply and prices across the continent.

"There's no food that we grow in a hurry," said Boelts, president of the Arizona Farm Bureau. "Beef takes years to produce. The lettuce you eat today? A farmer was working on how they would grow that crop six plus months ago."

Ray Martinez grows alfalfa on a reservation home to the Colorado River Indian Tribes. The tribe holds some of the river's oldest rights, and although its Arizona allocation is substantial, an aging irrigation system and a lack of infrastructure have kept much of the water out of reach. Martinez and the tribal water department are concerned about having enough water to finish the current growing season. He has left some fields unplanted for years to help prop up Lake Mead. If the reservoir continues to drop, he said, the surface water reaching him and neighboring farms will be further limited.

"Unfortunately, Mother Nature has its own way of doing things, and we have no control of that," he added.

What happens next will hinge in part on negotiations over longer-term river rules once the current federal plan expires, and on how courts weigh Nevada's challenge — outcomes that will shape water access for cities, tribes, and farms across the basin.

This story was originally featured on Fortune.com.