The conservation groups and the Confederate Tribes of the Goshute Reservation filed a petition with the U.S. Fish and Wildlife Service to list the shiny, 2 1/2-inch-long least chub for protection as a threatened or endangered species.

They cited the water authority's plans to pump up to 30,000 acre-feet of groundwater per year from Snake Valley, which straddles the Utah border in central Nevada.

"Of great concern for this species is future water withdrawals from the Snake Valley aquifer that are currently proposed to support human population growth in Southern Nevada," reads the 58-page petition by the Center for Biological Diversity, the Great Basin Chapter of Trout Unlimited, the tribes and the Sierra Club's Utah Chapter.

In a statement Wednesday, they said the least chub "has been reduced to just six fragile wild populations, three of which occur in the Snake Valley, where planned pumping of water for runaway growth in Las Vegas is a serious threat to the tiny fish's survival."

The petition describes other factors affecting the least chub, including non-native mosquito fish, livestock grazing and farming. But the greatest concern is the water authority's proposal to drill nine pumping stations in Snake Valley.

"The best science available so far tells us that groundwater withdrawal proposed in Snake Valley could potentially cause significant drawdown of the Snake Valley water table, with repercussions for all aquatic species and wetland systems that rely on consistent spring discharge," the petition reads.

"Repercussions in this case for the least chub could be catastrophic."

A spokesman for the Southern Nevada Water Authority said his agency's record for protecting species and the environment will prevail in persuading the U.S. Fish and Wildlife Service that the least chub's survival won't be impacted by groundwater pumping.

"The short answer is that there are already safeguards because of our agreement with federal agencies prior to pumping that should be able to protect that species," said the spokesman, J.C. Davis.

"Our commitment has been to protect that and other species, and that's what we're going to do," he said. "It shouldn't affect the viability of developing groundwater in Snake Valley. We have always developed water resources in an environmentally responsible manner.

"We have an awfully good track record for environmental stewardship," Davis said.

He said the water authority is "years away from pumping." In the meantime, safeguards to ensure monitoring and certain flow rates in the Snake Valley will become part of the Bureau of Land Management's environmental impact statement for the project.

In addition to Snake Valley, Davis said the impact statement will cover planned groundwater pumping in Spring Valley, Cave Valley, Dry Lake Valley and Delamar Valley.

Even if the least chub becomes listed for protection under the Endangered Species Act, Davis said the water authority would work out preservation measures through consultation with the U.S. Fish and Wildlife Service.

"At the end of the day, development of these groundwater sources and preservation of wildlife species are not mutually exclusive," he said.

Noah Greenwald, conservation biologist for the Center for Biological Diversity in Portland, Ore., said the petition should be a wake-up call for authorities in the Las Vegas Valley that they need to practice additional conservation measures and set limits on urban growth.

"At what point does Las Vegas stop sucking up water from other places?" he asked. "How far will Las Vegas go to get water to keep growing?"

"We hope the petition will make them seriously consider the wisdom of groundwater pumping from the area," Greenwald said.

Davis said the idea behind pumping groundwater in White Pine County is not so much to increase growth in the Las Vegas Valley but to ensure that the existing population will have a backup water supply should the drought continue along the Colorado River.

"The groundwater project is as much about protecting the people who live here now as it is about developing water supplies for the future," he said.

The amount proposed for pumping from Snake Valley, up to 30,000 acre-feet, is enough to support 60,000 homes, not counting what are known as return-flow credits, or the amount of treated wastewater returned to Lake Mead from use of that water.

Conservation measures targeting water used for the urban landscape have been effective, he noted. From 2002 to 2006, the valley's population increased by 330,000, but water consumption decreased by 18 billion gallons.

The gain was made by water agencies convincing customers to use less water on landscaping and getting credit for returning more treated wastewater to Lake Mead.

Don Duff, a former federal fisheries biologist and president of the Great Basin Chapter of Trout Unlimited, said the least chub is a cold-water species left over from ancient Lake Bonneville as it dried up thousands of years ago.

He said he fears groundwater pumping in Snake Valley will compound the effects that today's drought is having on springs vital to the chub's habitat.

Massive pumping proposed by the water authority, he said, could lower the Snake Valley aquifer by 40 feet to 50 feet between the first and second decade after pumping begins.

As it stands, stream flows at 2 cubic feet per second to 10 cubic feet per second are three times less than they should be this time of year.

"It's getting to be pretty critical from a scientific standpoint," he said by telephone from Salt Lake City. "The risk in the future is that groundwater pumping could draw down that aquifer so that all the springs go dry and the wild populations are lost."