LAS VEGAS —

       Trying to stave off dangerously low water levels in Lake Mead, officials in California, Arizona and Nevada have reached an agreement to significantly reduce the amount they take from the Colorado River.

       The problem took on new urgency this summer, when the federal government declared a first-ever water shortage in the 86-year-old lake near Las Vegas .

       The agreement, which was signed Wednesday after four months of negotiation, amounts to leaving leaving 1 million acre-feet of water in the lake over the next two years.

       Water agencies in Southern California, Arizona and Nevada agreed to find water-savings from various sources and split the $200-million cost with the federal government.

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       The Colorado River has been chronically overused, and its flows have shrunk dramatically over the past 22 years during a megadrought that research shows is worsened by global warming.

       In 2019, officials from the same states agreed to cutbacks aimed at reducing the risks of a crash at Lake Mead . But those proved insufficient as extremely hot, dry conditions have baked the Colorado River watershed, dramatically reducing flows.

       If the lake continues to drop, the Southwest could face larger cuts that would affect farms and cities throughout the region.

       “We’re experiencing what scientists are calling the new normal, a warmer, drier West,” the federal reclamation commissioner, Camille Calimlim Touton, said Wednesday during a speech that was livestreamed at the annual conference of the Colorado River Water Users Assn. “The basin is at a tipping point.”

       The Colorado River provides water for about 40 million people and farmlands from Wyoming to the U.S.-Mexico border. Rising temperatures and diminished snowpack have added to the punishing drought in the watershed.