SAN FRANCISCO (KCBS) _ It’s called Muir’s March after famed naturalist John Muir.

The seven day, 45-mile trek across Yosemite National Park is aimed at educating San Franciscans about the source of their tap water.

18 people departed on Sunday and they are expected to raise at least $30,000 for the eventual restoration of the Hetch Hetchy Reservoir.

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“The vast majority of San Franciscans have no idea where their water comes from. They think it comes from Hetch Hetchy,” said Mike Marshall, the executive director of Restore Hetch Hetchy. “They think their power is generated by the dam at Hetch Hetchy. But neither is true.”

Marshall said the water actually comes from the Tuolumne River.

“If we just educate folks to understand that their water will still come from the Tuolumne River, we just won’t use Yosemite National as a storage facility,” he said. “That changes their opinions.”

Marshall said the funds from the trek will go towards a public information campaign aimed at putting the issue of removing O’Shaughnessy Dam before San Francisco voters in 2011 or 2012.