Lake Mead, the reservoir formed by the Hoover Dam on the Colorado River, has hit its lowest water levels ever, according to government officials.
On Thursday morning, the surface elevation of Lake Mead along the Nevada-Arizona border dipped to 1,071.48 feet, data from the Bureau of Reclamation shows.
Officials expect the water levels to continue to decline until November, U.S. Bureau of Reclamation spokeswoman Patti Aaron told The Associated Press.
Last month, the U.S. Bureau of Reclamation projected that levels in man-made lakes that supply water for millions of people in the U.S. West and Mexico will shrink to historic lows.
The bureau is expected to release an official projection in August, which will determine the water deliveries to Arizona, California and Nevada in 2022. Water levels should begin to rebound in November, Aaron said.
The Colorado River supplies water to 40 million people, while the Hoover Dam generates electricity to about 25 million people.
The water levels could drop so low that the federal government could need to declare the first-ever official water shortage in Arizona and Nevada, prompting mandated cuts in water usage, The Associated Press reported.
ABC News' Matt Gutman contributed to this report.