Which man-made lake is the largest reservoir in the United States?

Lake Mead is the largest reservoir in the United States by water-storage capacity. It was created by Hoover Dam on the Colorado River along the Arizona–Nevada border.

Construction of Hoover Dam began during the 1930s, and Lake Mead began filling in 1935. At maximum capacity, the reservoir can hold about 28.23 million acre-feet of water and stretch for roughly 120 miles. It supplies water to Arizona, California, Nevada, and parts of Mexico, supporting cities, farms, and industry in the arid Southwest.

“Largest” can cause confusion because reservoirs may be compared by capacity, surface area, or the amount of water they currently contain. Lake Mead is the standard answer when the comparison means designed water-storage capacity. Its level changes substantially with drought, withdrawals, and snowmelt in the Colorado River basin.

Lake Powell, behind Glen Canyon Dam, is another enormous Colorado River reservoir and may appear in rankings using different measurements. Lake Oahe is also a major US reservoir, but it ranks below Lake Mead by volume.