The Sierra Club and other environmental groups hope to defeat a San Francisco ballot measure that would revamp and expand the aging Hetch Hetchy water system. Proposition A on the November ballot would approve a $1.6 billion bond measure that would help pay the $3.6 billion cost of rebuilding the aqueduct that delivers water from the Sierra Nevada to 2.4 million Bay Area customers. The Sierra Club and other groups say the project will divert 30% more water from the Tuolumne River and harm salmon and steelhead populations. City officials say that amount is closer to 10%. Not all environmentalists are united against the measure. The San Francisco League of Conservation Voters and the Green Party both endorse the bond measure.