The warnings came in a Wednesday hearing convened by the Senate Energy and Natural Resources Committee in the wake of a National Academies of Sciences report this spring that said the West is likely to suffer longer and more severe droughts from global warming.

Bradley Udall, director of an environmental research institute connected to the University of Colorado, said Lake Mead's 14 million acre-feet of water, or about 4.5 trillion gallons, isn't being replaced as fast as it is being used.

"At the current rate of use, Lake Mead has 10 years of water left in it," he said.

Southern Nevada Water Authority General Manager Pat Mulroy did not attend the hearing. She said Udall's conclusion represented the worst of worse-case scenarios for the Colorado River.

"Run a series of low-flow years (through a computer model), and it's possible. Not probable, but possible," Mulroy said.

"As a water manager, we have to look at the worst case possible."

Officials at the Bureau of Reclamation familiar with models of Lake Mead's future levels were unavailable on Friday.

But water authority spokesman Scott Huntley said it would be highly unlikely that Lake Mead would run dry in 10 years because water managers eventually would step in and restrict water usage to conserve.

Nevada and the six other Colorado River states have sent the Interior Department a landmark water supply plan that, if approved, will put measures in place to keep Lake Mead's level steady if the drought worsens.

Water officials say the plan represents the most comprehensive set of operating guidelines in the history of the Colorado River. It includes a water shortage agreement between Nevada and Arizona and puts in place a concept called "intentionally created surplus" to keep more water in Lake Mead, Lake Powell and other reservoirs on the river and allow them to recover more quickly from drought.

For example, water for agriculture in Southern California can be kept or "banked" for future use in Lake Mead if crop lands are allowed to go fallow.

The Las Vegas Valley gets about 90 percent of its drinking water supply from the Colorado River by way of Lake Mead.

Predictions such as Udall's have prompted Mulroy's agency to accelerate its work on a controversial $2 billion pipeline network that would supply growth in Las Vegas with groundwater from across Eastern Nevada.

"We have to diversify where our water comes from," Mulroy said.

Tim Brick, chairman of the Metropolitan Water District of Southern California, said the strength of the Colorado River, the primary artery that feeds Lake Mead, could decrease by 15 percent at current rates in the near future.

According to Brick's written testimony, reservoirs in the Colorado River's Upper Basin, which includes Colorado, New Mexico and Utah, are at their lowest levels since their initial fillings decades ago.

"It is a great deal, a great deal of concern," he said.

Terry Fulp, Boulder Canyon operations manager at the Bureau of Reclamation, said at Wednesday's hearing that drought, floods and other climate phenomena are factored into management of the lake.

The agency would need to see more dramatic changes to Colorado River volumes before making substantial changes in its operations, he said.

"We do not believe that operational changes to release patterns or storage levels at major water facilities are warranted at this time," Fulp said, adding that the agency is an active partner in climate research.

The new operational rules developed by federal officials and water managers from the seven states that share the river could be in place by the end of the year.

Mulroy said the rules are designed to provide "absolute protection" for Lake Mead so that it does not shrink below a minimum level needed to keep water flowing to Southern Nevada and hydropower flowing from Hoover Dam.

But Mother Nature might have other ideas.

Mulroy said the new operating scheme simply won't work if the Colorado's flow shrinks further and stays that way for an extended period.

"At this point, it's anybody's guess. We're just in the midst of an ugly, ugly drought," she said.