7/7/10 When researchers wanted to test largemouth bass at Lower Crystal Springs Reservoir for mercury levels, the reservoir's managers in San Francisco figured the scientists were simply looking for a clean sample to compare with toxic results at other spots.

Instead, the study showed that the fish in the San Mateo County lake - which collects rainwater as well as water piped in from Yosemite's Hetch Hetchy reservoir - had some of the highest mercury levels in the state.

Now, the San Francisco Public Utilities Commission, which oversees Crystal Springs and the rest of the sprawling network that supplies drinking water to 2.5 million people in San Francisco, San Mateo, Santa Clara and Alameda counties, is trying to find the source of the heavy metal, a neurotoxin that can cause developmental damage in children and brain, lung and kidney problems in adults.

"It was a big surprise," said Tim Ramirez, manager for natural resources and land management at the commission's water enterprise division. "We're going to jump on it and try to find out what's going on."

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