Bay Area beaches received mostly high marks for water quality in a report card released today by the environmental group Heal the Bay.
Of the graded ocean-side beaches from Marin County to San Mateo County, 38 of 40 received an A grade for the high-traffic summer period of April to October.
That's 95 percent, 2 percent higher than a five-year average for the beaches during the summer period.
While the overall report was favorable, three local beaches are on the state's list of the 10 most polluted beaches based on levels of harmful bacteria.
The harmful bacteria can cause illnesses such as stomach flu, ear infections, upper respiratory infections, and skin rashes among people who go in the water, according to Heal the Bay.
Cowell Beach at the wharf in Santa Cruz County is the No. 1 most polluted beach in the state, Heal the Bay's report said.
Part of the problem at Cowell Beach is birds roosting. Work has started to install steel fencing to prevent the roosting.
The other two beaches to make the list of the top 10 most polluted beaches are Pillar Point Harbor in San Mateo County and Sunnydale Cove near Candlestick Point in San Francisco.
Both beaches have poor water circulation, Heal the Bay spokesman James Alamillo said.
Heal the Bay officials said El Nino contributed to poor water quality grades at some beaches this past winter because high amounts of rainfall can cause older sewer systems to inadvertently release under-treated sewage into the Bay or ocean.
Beach water quality is graded each week and the grades can be found at beachreportcard.org.
Beaches facing San Francisco Bay had lower grades overall than ocean-side beaches. Twenty-four of 28 Bayside beaches, or 85 percent, received A or B grades, according to the report card.
In Sonoma County, all seven monitored beaches received grades of A+.
During last summer's reporting season, California's drought was a major contributor to better grades because less rainfall meant less runoff into bodies of water.
Heal the Bay officials warn that swimmers should wait at least three days after a rain before swimming. They also warn beachgoers to avoid going in the water at beaches that are cut off from the ocean or Bay.
Also, swimmers should swim at least 100 yards from working storm drains and piers.
Bay Area beaches receive mostly high grades for water quality