The group, Heal the Bay, presented its 22nd annual Beach Report Card. Most of it is good news.
During dry weather, 98 percent of beaches from Marin County to San Mateo County get good or excellent grades. But bacterial contamination from sewage runoff peaks during wet weather.
The main problem areas are along the Peninsula, especially Pillar Point Harbor, Oyster Point, Aquatic Park and Lakeshore Park.
"When it rains, they get into these leaky sewer pipes, they overwhelm the treatment systems which cause backups and sewage spills into storm drains and local creeks that ultimately get into the bay," said Eliet Henderson with San Francisco Baykeeper.
No Bay Area sites are in the top 10 most contaminated beaches. Those are all located in Southern California, most near Malibu.