The Colorado River Basin has seen a staggering amount of water evaporate over the past two decades, equaling the amount of water in the country’s largest reservoir, Lake Mead.

A study of satellite images from Arizona State University found that the waterway has lost 27.8 million acre-feet of groundwater between 2002 and 2024. The reduction is likely due to an increased dependency on surface water from Lake Mead near Las Vegas by six states, Native American tribal regions, and parts of Mexico.

“If we want our great-great-great-grandchildren to eat, then it’s time to think more holistically about the water that we use and what kind of protection it needs,” a co-author of the ASU study, Jay Famiglietti, said to the Las Vegas Review-Journal. “Groundwater is key to our economic vitality, yet it remains sort of spottedly managed.” 

With groundwater’s use largely under-regulated, more states have been tapping into it as a resource. Arizona has often been cited as the biggest offender, due to its heavy dependence on groundwater for its $1.4 billion agricultural industry. Only 18 percent of the state’s groundwater is regulated.

In 2023, lawmakers in the Phoenix area rejected new housing construction due to a lack of available water to support future growth. Arizona’s governor, Katie Hobbs, cited projections at the time that the demand for groundwater in the Phoenix area would outpace supplies by 4.9 million acre-feet.

“The main message is that we are giving a lot of attention to surface water along the Colorado River, but groundwater needs a lot of attention as it is getting depleted in huge amounts,” the study’s lead author, Karem Abdelmohsen, said to the Review-Journal.

 “We need to slow down and give a chance for nature to refill our aquifers.”