But the state also is studying dams, drawing opposition from some environmentalists, particularly a group called the Center for Environmental Law and Policy.

"Our water future doesn't lie with new dams," said Dr. John Osborn, a Spokane physician and chairman of the Sierra Club chapter in Spokane. "It's water conservation."

Osborn contends dam boosters are pushing for new dams to benefit business, underplaying the costs and environmental destruction and ignoring the benefits of improving conservation.

In other states:

• Four major water storage projects are being studied in California, including a proposal for a new dam on the San Joaquin River, said Sue McClurg, of the Water Education Foundation in Sacramento. Republicans in the California Assembly say they will block any plan to improve water supplies that doesn't include new dams.

• The Southern Nevada Water Authority, which serves Las Vegas, is considering a reservoir to capture more Colorado River water before it flows into Mexico.

• In Colorado, there is a proposal to create two new reservoirs on the Yampa River.

• Some in Idaho still hope to rebuild the Teton Dam, which collapsed in 1976, killing 11 people.

A major barrier to new dams is cost, which runs into the billions, Manning said. It's uncertain how much the federal government would be willing to pay.

A recent study of the Black Rock dam proposal in the Yakima River basin concludes the 600-foot-high dam would cost $6.7 billion to build and operate, and would return just 16 cents for every dollar spent.

The explosive growth of the West is in part a product of a binge in dam construction that provided plentiful water and cheap electricity. The U.S. Bureau of Reclamation built more than 472 dams, including Shasta in California, Bonneville on the Oregon-Washington state line, Fort Peck Dam in Montana and Grand Coulee Dam in Washington.

But the era of giant dams essentially ended with the Glen Canyon Dam, just upstream from the Grand Canyon on the Arizona-Utah state line, which galvanized the environmental movement because its Lake Powell inundated a huge swath of scenic land, archaeological sites and places important to native Americans.

Lake Powell and its downstream cousin, Lake Mead — two of the nation's largest manmade reservoirs — provide water for millions of people in Nevada, Arizona and California.

However, both lakes are only half full after years of drought, and researchers at San Diego's Scripps Institution of Oceanography figure climate change and growing demand could drain them within just 13 years.