Low water levels of Lake Mead are seen near the Hoover Dam on the Nevada and Arizona border, April 11, 2015. Reuters

A white band hems the shoreline of Lake Mead like a bathtub ring, a stark reminder that the nation’s largest reservoir is steadily losing water at a time when the precious commodity is needed the most. The latest measurements released Wednesday show the lake is nearing its lowest height in its 80-year existence. At nearly 1,081 feet, Lake Mead’s water level is 148 feet below capacity and dropping -- an elevation not seen since 1937, according to the U.S. Department of the Interior’s Bureau of Reclamation.

Lake Mead’s plight is a symbol of the crippling “mega drought” that has gripped California and other Southwest states for the past four years, with no sign of letting up. Scientists are calling the water shortage the worst in centuries. "Even at the middle-of-the-road scenario, we see enough warming and drying to push us past the worst droughts experienced in the region since the medieval era," Benjamin Cook, a scientist at NASA's Goddard Institute for Space Studies in New York, told National Geographic in February.

In southern California, once green hillsides have turned brown. Fifty million square feet of lawns are slated to be replaced with drought-resistant plants. Residents and businesses face increasingly tougher water use restrictions, and lawmakers are scrambling to find new ways to create usable water -- including building a $1 billion desalination plant near San Diego -- as the state’s critical supplies run dry. Many of the state’s crucial reservoirs are now at a third of capacity. Officials have begun tapping groundwater, but even that won’t last forever. Scientists predict California will need 11 trillion gallons of water to recover from the drought -- the equivalent of 1 1/2 Lake Meads.

The water level in Lake Mead approaches its lowest height in 80 years. Reuters
People take photos near Hoover Dam on the Nevada and Arizona border, April 11, 2015. Reuters
Hoover Dam and Lake Mead on the Nevada and Arizona border, April 11, 2015. Reuters

Lake Mead is located about 24 miles southeast of Las Vegas, a bulge in the Colorado River that provides water to residents and businesses in Arizona, southern California, southern Nevada and northern Mexico. It was created in the 1930s with the construction of the Hoover Dam.

At its peak, Lake Mead’s water level topped off at about 1,223.44 feet. That was 32 years ago. Today, the lake is losing elevation at a rate of about 2.16 inches every 24 hours. Officials predict that it will hit 1,075 feet by May 31.

Lake Mead’s water elevation has always fluctuated with the seasons, but over the past three decades, every time the water level has dipped, its rebound has been less than adequate. Nearly all of the water in Lake Mead comes from snowmelt from Colorado, Utah, New Mexico and Wyoming. Disappointing rainy seasons and low snowpack in those areas have meant that the water that once replenished Lake Mead at the end of every winter has slowed to a trickle.

Lawmakers in California have set out to limit the state’s water use through new and tougher restrictions. Officials hope to cut the state’s water usage by 25 percent over the coming year. "We are standing on dry grass, and we should be standing on five feet of snow," California Gov. Jerry Brown said earlier this month during a press briefing at Echo Summit in California’s Sierra Nevada. "We're in a historic drought, and that demands unprecedented action."

Brown continued: "People should realize we're in a new era. The idea of your nice little green grass getting lots of water every day, that's going to be a thing of the past. We're not going to change everything overnight, but we are in a transition period. People have to realize that in many parts of California, they are living in a desert."