Proponents of removing the dam on Hetch Hetchy Reservoir said Friday that they are ready to turn in signatures to force a vote on the issue in San Francisco.
They have scheduled a Monday afternoon news conference outside City Hall to announce that they have collected about 15,000 signatures from registered voters.
The proposal would go on the Nov. 6 ballot if election officials verify at least 9,702 of the names.
The measure would direct city officials to study alternatives to the controversial reservoir on the Tuolumne River in Yosemite National Park.
The detailed plan, which could involve enlarging Don Pedro Reservoir downstream on the same river, would go before San Francisco voters in 2016.
The campaign is led by Restore Hetch Hetchy, which aims to turn Hetch Hetchy Valley back to what it was before San Francisco dammed it for water and power about 90 years ago. Sierra Club founder John Muir, who died shortly after the approval, likened the scenic area to Yosemite Valley.
Critics of the effort generally agree that a dam should not have been allowed in a national park. But they say removing it would be a costly and unwise move at a time when the drought-prone state should be adding water storage.
The opponents include the Modesto and Turlock irrigation districts, which jointly own Don Pedro.
Restore Hetch Hetchy also proposes water conservation measures, recycling and other steps to help San Francisco meet its needs.
The debate coincides with discussion over a proposal to sell some of the MID's water to San Francisco. This water would be diverted at Hetch Hetchy Reservoir.
The MID board has scheduled a July 24 vote on the first sale of 2,240 acre-feet per year, about 1 percent of its average deliveries. The board also could launch the environmental study needed for the sale of another 25,000 acre-feet freed up by conservation projects on the canals.