(Bloomberg) -- Arizona, which grows most of the lettuce eaten in the US each winter, will be losing about a fifth of the water it gets from the Colorado River as drought and climate change diminish the key water basin.

The US will withhold 21% of Arizona’s annual water allocation from the Colorado River in 2023 as part of conservation efforts announced Tuesday by the Interior Department’s Bureau of Reclamation. The measure is the latest action aimed at dealing with the first-ever water shortage in the river basin. Lake Mead and Lake Powell -- the two largest US reservoirs -- stand at historically low levels and combined are at 28% of their capacity, officials said.

Farmers in Arizona, who provide more than 90% of the US’s leafy greens each November through March, have already borne the brunt of prior cuts, along with those who make a living from the state’s $23.3 billion agriculture industry. Pinal County, between Phoenix and Tucson, is likely to be hit especially hard since the area known for cotton and livestock has already seen about half its farmland go idle due to prior water reductions.

“The system is approaching a tipping point,” Bureau of Reclamation Commissioner Camille Calimlim Touton, told reporters Tuesday. “Without action we can’t protect the system and the millions of Americans who rely on this critical resource.”

Interior Department officials also announced an 8% reduction to Nevada and 7% cut to Mexico’s share of river, which flows 1,450 miles from Colorado into northern Mexico and is relied upon by 40 million people. The cuts are initially from Lake Mead, the reservoir on the Nevada-Arizona border formed by Hoover Dam.

Read more: Drought punishes west anew as US cuts Colorado River water 

California, the biggest US agriculture producer, wasn’t hit with cuts. As a holder of so-called senior water rights, conditions aren’t yet severe enough to trigger reductions. That doesn’t mean the historic drought isn’t taking a toll. Farmers in the northern and central parts of the state have already seen their allocations slashed from other water sources, and growers in southern California who rely on the Colorado River remain nervous about future decreases. 

Arizona in the meantime is making it clear that collaboration is urgently needed across the region. 

“While we agree that it is necessary to take drastic measures to protect the river, Arizona cannot continue to bear an out-sized share of these measures without help from other partners,” the Arizona Farm Bureau said in a statement. 

The Bureau of Reclamation announced plans in May to withhold 480,000 acre feet of water in Lake Powell, the artificial reservoir that straddles Utah and Arizona. The agency said Tuesday it would consider taking additional steps next April after evaluating drought conditions and water levels.

The western US power market is also on the front line. There is a chance that Lake Powell could drop to the point next summer where the Glen Canyon Dam wouldn’t be able to produce electricity, officials said.

Hoover Dam produces enough power for 1.3 million people in Nevada, Arizona and California. Glen Canyon Dam produces enough power for about 5 million customers in Arizona, Colorado, Nevada, New Mexico, Utah and Wyoming.


(Updates with details in the sixth paragraph and comment in the eighth.)

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