For the first time ever, there’s an official water shortage at the largest water reservoir in the US. Today, the US Bureau of Reclamation declared a water shortage at Hoover Dam’s Lake Mead, which 25 million people across the Western US and Mexico rely on for water. It’s the first time this kind of declaration had been madeon the Colorado River, the main source of water for Lake Mead, CNN and E&E News report.

The declaration will trigger mandatory cuts to water use starting January 1, 2023. California, Arizona, and Nevada all tap water from Lake Mead. Based on federal guidelines for shortages brokered in 2019, Arizona will lose 18 percent of its annual apportionment of water from Lake Mead, and Nevada will lose seven percent of their annual allotment. Mexico, which also gets water from the watershed, will lose five percent of its share. California won’t face cuts just yet, because it has stronger water rights under complex water sharing agreements.