A white 'bathtub ring' encircles Lake Mead as the water continues falling to historic low levels on September 24, 2004 near Boulder City, Nevada. The desert city of Las Vegas could face serious water shortage if the five-year-old Western drought continues to shrink the Colorado River. The drought has exposed long-submerged landscapes to direct sunlight for the first time in decades. The river provides water for 25 million people, millions of acres of farmland, and an assortment of endangered and other animals. It could take a 10-year run of average rain and snow to refill the reservoirs.