San Mateo County beaches are the second-worst in California when it comes to a key measure of bacterial pollution, according to a report released Wednesday by the Natural Resources Defense Council.

Contra Costa County's beaches were the worst, the report found. But the sample size for Contra Costa County was small -- only two monitoring sites, the north and south ends of Richmond's Keller Beach, were included in the report. San Mateo County, meanwhile, contributed data from 45 sites at beaches on the bay and along the Pacific Ocean.

The beaches in these counties exceeded daily maximum levels for E. coli and other bacteria in 2012 more often than any other counties in the state, the report found. California ranked 20th of 30 coastal states, including those surrounding the Great Lakes.

Stormwater runoff and sewage spills are the primary causes of bacterial pollution on beaches, according to the Natural Resources Defense Council, which based its annual "Testing the Waters" report on water-quality data from more than 3,000 beach sites across the country. Citing a 2001 analysis by the U.S. Environmental Protection Agency, the council claims as many as 3.5 million Americans -- and possibly more -- become ill every year by coming into contact with pollution from these sources.

"Stormwater pollution remains a persistent problem on our coasts and beaches," said Noah Garrison, a California attorney with the council, "and it's certainly a

Most polluted

Keller Beach formed the basis for Contra Costa County's poor showing in the report. Two monitoring sites exceeded bacteria thresholds a combined 17.3 percent of the time.

San Mateo County had a far greater data sample, but its 16.5 percent violation rate was driven by a trio of chronic offenders in terms of water quality: Parkside Aquatic Park and Lakeshore Park, two lagoon beaches in San Mateo, and Pillar Point Harbor north of Half Moon Bay.

One segment of the beach at Pillar Point Harbor had some of the highest violation rates in the state. Pillar Point-Capistrano, measured twice a month, exceeded public health standards for bacteria 52 percent of the time in 2012.

Sabrina Brennan, a member of the San Mateo County Harbor District board, said fecal contamination at Pillar Point is a long-standing issue, and a study on the subject is wrapping up. Brennan said she advises people not to let their children play at the Capistrano segment.

Follow this link:

Contra Costa, San Mateo County beaches rife with bacteria, report says