But they say the most controversial proposal - draining Lake Powell - will be left off the table when the planning process begins in earnest.

With water levels at both Lake Powell and Lake Mead still near historic lows because of a drought that has lasted most of the decade, environmental groups in recent years have proposed decommissioning Glen Canyon Dam. Water from Lake Powell would be moved to a series of depleted aquifers in the region, leaving Mead as the lower Colorado River's primary reservoir.

Such an undertaking, environmentalists say, would not only save water that is now lost to evaporation and seepage in Lake Powell, but restore the lower Colorado River, particularly its course through the Grand Canyon, to a more natural state.

"Decommissioning Glen Canyon Dam, and allowing nature to do what was done for years would be in the best interest of Grand Canyon National Park," said Jon Weisheit, conservation director for the Moab-based Living Rivers, which submitted a proposal entitled "The One Dam Solution" to the bureau.

"By eliminating evaporation, an additional 800,000 acre-feet of water would [annually] be available to the lower basin states," he noted, referring to Arizona, Nevada and California. "We think that's significant."

However, Randy Peterson, the bureau's regional manager for environmental resources, who directed a hearing Thursday in Salt Lake City, said there is no chance the proposal will be considered.

"The last two administrations have made it pretty clear that they are not interested in decommissioning Glen Canyon Dam," said Peterson. "So it's not a partisan issue. Each administration has made it pretty clear how important Lake Powell and Lake Mead are to the lower basin states. If not for Glen Canyon Dam and Lake Powell, Lake Mead would be nearly empty right now. The last five years have shown why the reservoir is needed."

Bureau officials have greeted another conservation proposal more enthusiastically. A consortium of environmental groups, including the Sierra Club, Pacific Institute, Sonoran Institute and Defenders of Wildlife have put forth a plan, called "Conservation Before Shortage," which would implement a series of conservation "triggers" on Lake Mead as the reservoir's water elevation decreases - with each trigger requiring the conservation of 200,000 acre-feet.

"Those impacted would be compensated," said Sierra Club member Jim Wechsler. "Funding would be partially paid by the federal government, the rest through surcharges on power and water use."

The plan, he continued, would help create certainty for water users, increase power production and maintain Mead's water level above the power pool minimum. The net result: more water in the Colorado River itself, which in turn would benefit the river's wildlife populations and habitats.

"It's another way to conserve by reducing demand," said Peterson.

Thanks to a very wet winter and spring, water levels in both Lake Powell and Lake Mead have been on the rise this summer, with Powell up 52 feet from its April low, and Mead up a more modest 14 feet.

Not a moment too soon, according to Glen Canyon National Recreation Area Superintendent Kitty Roberts, who says people don't realize how close the National Park Service was to curtailing recreation on Powell altogether earlier this year.

"We were right at the edge," she said.

But environmentalist Weisheit says it's only a matter of time until officials face the edge again, with sediment pushing closer and closer to Glen Canyon Dam because of the low water levels.

And he is critical of an ongoing congressional rider - inserted by the Utah delegation - that prohibits any study of the long-term future of the dam and Lake Powell.

"If Glen Canyon Dam is necessary, studies will prove it," he said. "Let science decide."

jbaird@sltrib.com