Northern California beaches scored high on an annual report card on water quality, but three of them in particular didn't fare well at all.

Cowell Beach in Santa Cruz was named the No. 1 "Beach Bummer" by Santa Monica-based Heal the Bay, which released its study today of bacteria in water samples from beaches around the state. While more than four out of five beaches in the Bay Area received a grade of "A", the group says pockets of pollution exist.

The other two local oceanside bummers listed are Baker Beach at Lobos Creek in San Francisco and Capitola Beach in Santa Cruz.

Amanda Griesbach, a water-quality scientist with Heal the Bay, told KQED's Mina Kim that swimming in dirty water can cause a range of illnesses. "You can get a skin infection an ear infection, eye infection," she said. "The most common is a GI infection (causing) stomach, diarrhea."

You can look at the whole report for all of California as a .pdf file, or check out the county-by-county grades on the web. Keep in mind the default data you'll see when you click on each beach relates to the most recent 30-day period of measurement; you have to click on the "historical data" tab to get a picture of an individual beach's health over the course of the year.

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For instance, Baker Beach Lobos Creek, a top-ten polluted beach, gets an A+ rating for the 30 days ending May 16, but an F overall because of its long periods of failing grades during the previous 12 months.

Here's more about the report from the group's FAQ:

Heal the Bay’s Beach Report Card is the only comprehensive analysis of coastline water quality in California. We monitor more than 350 beaches weekly from Oregon to the Mexico border, assigning an A to F grade based on the health risks of swimming or surfing at that location. On our website, you can find out which beaches are safe and unsafe, check recent water quality history and look up details of current and past beach closures.

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Santa Cruz' Cowell Beach Named Most Polluted in State; Look Up Health of Your Local Beach Online