President Donald Trump has signed a plan to cut back on the use of water from the Colorado River, which serves 40 million people in the U.S. West.
Trump announced the action Tuesday on Twitter.
The Colorado River drought contingency plan aims to keep two key reservoirs from falling so low they cannot deliver water or produce hydropower. It was negotiated among the seven states that draw water from the river.
Mexico also agreed to store water in Lake Mead on the Arizona-Nevada border if the U.S. legislation was approved by April 22.
Arizona has the lowest-priority access to Colorado River water and will be hit hardest. The state negotiated a separate agreement to provide other water sources and new groundwater infrastructure for farmers between Phoenix and Tucson.