Efforts to take out Yosemite dam raise questions of cost, quality.(Knight Ridder Newspapers)

YOSEMITE NATIONAL PARK, Calif. _ John Muir called Hetch Hetchy the "wonderfully exact counterpart" to Yosemite Valley.

Even today, with Hetch Hetchy's floor 300 feet under water, it is easy to see why.

Out of the reservoir on the right rises a rounded half dome of towering rock. On the left, a wall of jutting granite resembles El Capitan.

Now, the most serious effort in more than a decade is under way to empty the reservoir and return Hetch Hetchy to its natural state.

The long-shot campaign comes in response to a multibillion-dollar initiative to fix the Hetch Hetchy water system, a plan that would be partly financed by a $1.6 billion bond issue on San Francisco's Nov. 5 ballot.

Supporters say it makes sense to consider taking out the dam and storing the water elsewhere before spending billions on an aging water system.

"This opportunity we have to allow nature to create another Yosemite Valley, there is no other opportunity like this anywhere on Earth," said Ron Good, executive director of Restore Hetch Hetchy.