Lake Mead and Lake Powell, the two largest reservoirs in the U.S., have both hit record-low water levels, with combined storage the lowest since 1957. Lake Mead sits along the Nevada-Arizona border near Las Vegas, and Lake Powell sits along the Utah-Arizona border, both fed by the Colorado River. Together, they supply water and power to 40 million people across the West, and both lakes are still dropping amid a 25-year megadrought.