SACRAMENTO -- Sport fish from rivers and streams in the Sacramento-San Joaquin Delta have higher levels of mercury in their systems than fish taken from anywhere else in California, a new survey has found.
Researchers for the State Water Resources Control Board in 2011 surveyed 16 species from 63 locations. The study found that Sacramento pikeminnow, smallmouth, largemouth and striped bass from the Delta watershed had the highest concentrations of mercury in their tissues, The Sacramento Bee reported Sunday.
The state's Office of Environmental Health Hazard Assessment lists mercury as unsafe for frequent consumption, especially for children and women of childbearing age. Studies have shown that even low doses can affect a child's motor skills and cause learning disabilities. Mercury also has been blamed for fertility and memory problems in adults.
Freshwater fish in California have absorbed mercury that leached into waterways from 19th and early 20th Century mines.
The sites with the most contaminated fish included fishing spots on the American and San Joaquin rivers, including Coloma, Discovery Park in Sacramento, the pier at Point Antioch and Louis Park in Stockton.
Many of the locations already have signs warning anglers of potential health hazards.
But UC Davis researcher Fraser Shilling tells the Bee that some people ignore the advisories and nonetheless consume what they catch. Shilling surveyed people who


fish rivers in Sacramento, Stockton and Suisun Bay about their catching and eating habits in 2008. He concluded that about 75,000 people consume enough fish from those areas to put them at risk, while about 8,500 eat about 10 times the amount that officials consider safe.
"This behavior may have a lot to do with a strong cultural preference for fish for economic reasons," Shilling said. "Once you buy your license, the fish becomes a free source of food. And in the lower elevations -- closer to the urban areas -- immigrants and ethnic minorities tend to be the main people catching fish."
Along with mercury, the Delta yielded fish with higher concentrations of PCBs -- chemicals that were used widely in paints and plastics before they were banned in 1979 -- and the insecticides dieldrin and DDT.