Lake Mead, the enormous reservoir of Colorado River water that hydrates Arizona, Nevada, California and northern Mexico, is receding to a level not seen since it was first being filled in the 1930s, stoking existential fears about water supply in the parched Southwest.
Heightening those concerns are recent signs that the region's record-breaking, 11-year drought could wear on for another year or longer. July not only saw the lake drop to 1956 levels but also brought cooling temperatures in the Pacific Ocean that signaled a developing La Niña system, historically a harbinger of more hot and dry weather.
The La Niña "appears to be strong, and it might even last two years," said Brad Udall, director of the National Oceanic and Atmospheric Administration's Western Water Assessment program at the University of Colorado.
In the 75 years since the workers began to hold back the Colorado River behind the Hoover Dam, the lake's water has taken two precipitous plunges: first during the prolonged drought of the 1950s, which ranks second only to the current dry spell, and again in the mid-1960s, when water managers began filling Mead's cousin 250 miles upstream, Lake Powell.
Neither dip was as severe or prolonged as that of the past decade. Nearly full in 1999, Mead has shrunken to 40 percent capacity, causing the ominous, bleach-white bathtub ring on the surrounding mountainsides to grow taller by the year. In the past five months, the lake steadily shed another 15 feet, to about 1,087 feet above sea level today. Four more feet and the lake surface will hit what would be the lowest mark since 1937 -- something the government projects will happen in October.