Last Sunday Lake Mead, created by the construction of Hoover Dam, dropped to its lowest level since the reservoir was filled 75 years ago. The water level is only 8 feet shy of reaching “critical water shortage status,” which will trigger a temporary distribution plan that will reduce water deliveries from the lake to Arizona and Nevada.

The lake’s low levels are a product of two factors: rapidly increasing demand, and decreasing flows in the Colorado River. The population of Las Vegas, which relies largely on the lake for its water supply, has grown from 5,165 to 2 million people since 1930. At the same time, the Southwest is experiencing a decade-long drought that scientists are acknowledging is a “recurrent and integral feature of the region’s climate” – and one that will be exacerbated by climate change. Since drought took hold on the Colorado and its tributaries in 1999, the surface of the lake has plunged almost 130 feet.

If the water level drops 33 feet from its current level, it will make it impossible to run the Hoover Dam’s massive hydroelectric turbines which provide power to the region. According to Pat Mulroy, the general manager of the Southern Nevada Water Authority, “if the flow continues downward and we can’t build back up supply, Las Vegas is in big trouble.” In 2009, 61 percent of San Diego’s water supply came from Lake Mead. However, unlike Arizona and Nevada, California will not hit with mandatory rationing due to its higher senior water rights. If the water level in Lake Mead falls 60 feet, California’s right to the reservoir’s water will be renegotiated.