LAS VEGAS -- The forecast for Lake Mead isn't looking good.

A new study warns the lake could dry up by the year 2021.

As water levels at Lake Mead recede, a new study warns it could get worse.

“The Scripps report is a wake-up call to Southern Nevada,” said Southern Nevada Water Authority general manager Pat Mulroy.

In this new report, scientists said Lake Mead has a 50 percent chance of drying in 13 years.

Their findings are based on global warming, the drought, water demand and how it's managed.

“It is a bad thing, where it doesn't appear there’s a real good side to it,” said Tim Barnett of the University of California, San Diego Scripps Institute of Oceanography.

“We are doing everything humanly possible to prepare for the possibility,” Mulroy said.

The SNWA manages the Valley's water and said 90 percent of that water comes from Lake Mead.

“We're in the process of building a third intake, but pumping, because it’s very difficult at those lower elevations. So, we as basin states, we will do everything we can to prevent Lake Mead from dropping below 1,000 feet. So, we'll reconvene and make some deeper, heavier cuts,” Mulroy said.

But some watchdog groups said the water authority and local municipalities aren't doing enough.

“We need to have a conservation that is not dictated by the developers. The developers are running the show right now,” said Launce Rake of the Progressive Leadership Alliance of Nevada.

Researchers with the study offer a possible solution.

“We might want to slow down building cities in the desert where they have a single water supply, and that's unreliable,” said Barnett.

Lake Mead officials said they were not part of the study, and the chances are slim the lake would ever dry up, because local agencies would never let that happen.