Lake Mead will need more than just rainfall to replenish itself, an expert has told Newsweek.

Spread between Nevada and Arizona—Lake Mead, the largest man-made reservoir in the U.S.—is best known for its rapidly declining water levels due to the ongoing megadrought gripping the western states. The lake is integral to surrounding communities, as it is also formed by the Hoover Dam on the Colorado River—which generates electricity for thousands of people. If the water levels continue to decline, the consequences could be catastrophic.