Lake Mead is the main reservoir formed by Hoover Dam in Southern Nevada.

Created in the 1930s as part of Hoover Dam [see also Elwood Mead], Lake Mead provides water storage in the Lower Basin of the Colorado River. The reservoir can hold 28,945,000 acre-feet’s capacity and at 248 square miles its capacity is the largest in United States.

Most of the water in Lake Mead is drawn from Rocky Mountain snowmelt and runoff.

However, one of the largest droughts on record in the region dating back to 2000 has lowered Lake Mead’s water level. Combined storage at Lake Mead and Lake Powell is down 50 percent. Meanwhile, Lake Mead loses roughly 800,000 acre-feet of water annually through evaporation.

These water supply concerns have a ripple effect, including on recreation and on water allocation to Arizona, California, and Nevada.

For instance, if Lake Mead’s water levels drop to 1,075 feet a water shortage would be declared in the Lower Basin.  A water shortage declaration would then reduce the annual amount of water sent to Arizona and Nevada.

A bountiful Rocky Mountain snow pack in 2016 – 2017 meant that there would be no risk of a shortage declaration on the Colorado River in 2018. A water year that was 113 percent of average raised capacity throughout the Colorado River Storage Project to 57 percent. It is estimated there is a 31 percent chance of a shortage declaration in January 2019.

The Bureau of Reclamation oversees Lake Mead as well as Hoover Dam. The National Park Service oversees recreational activities as part of the Lake Mead National Recreation Area.

Lake Mead Agreements

In 2007, the Seven States Agreement and subsequent federal Record of Decision established new guidelines for both Lake Powell and Lake Mead. The agreement includes rules to allow Arizona, California, and Nevada to store conserved water in Lake Mead.

In 2012, Minute 319 was signed between the United State and Mexico. Minute 319 establishes new rules for sharing Colorado River water. Under the 5-year agreement—one in a series of U.S.-Mexico Colorado River agreements dating back to 1944—Mexico may store some of its of Colorado River water in Lake Mead. However, if a water shortage is declared in the Lower Basin, less water will be sent to Mexico. Minute 319 could also provide a template for future long-term water management policies.

In 2017, U.S. and Mexican representatives with the International Boundary and Water Commission signed Minute 323, which enables Mexico to continue to store its water in Lake Mead, helping to keep reservoir levels high enough to avoid triggering dramatic cuts to Colorado River water users.