(05-22) 10:34 PDT San Francisco -- There might be one upside to the drought, and it's just in time for the holiday weekend.

Bay Area beaches are cleaner and healthier than ever, because so little rain has washed dangerous bacteria and other pathogens into San Francisco Bay and the Pacific coastline, according to a report released Thursday by Heal the Bay.

"Dry weather has meant less urban runoff. This is all great heading into Memorial Day weekend, but we shouldn't have a false sense of security," said Amanda Griesbach, a water quality scientist for Heal the Bay, a Santa Monica-based environmental group. "Next year, especially if we have an El Nio cycle, things could be very different."

Heal the Bay's 24th annual survey of 650 West Coast beaches showed some of the highest-ever grades for cleanliness, with 95 percent of California's beaches receiving "excellent" or "good" marks.

The group looked at the amounts of harmful bacteria from sewage leaks, pollution runoff and industry, pathogens that are flushed into creeks and storm drains and ultimately onto the beaches.

When people or wildlife come into contact with the bacteria, they're likely to suffer from gastro-intestinal problems like diarrhea, skin rashes or eye, ear or lung infections.

In San Francisco, the beaches with the highest grades include Aquatic Beach at the Hyde Street Pier, Ocean Beach at Balboa Avenue and Baker Beach.

Most Marin and East Bay beaches also received high scores.

The Peninsula saw some challenges. Marina Lagoon in San Mateo is a perpetual low-scorer, and 2013-14 was no exception. In fact, it ranked as the second-worst beach in the state, largely because it's enclosed and shallow and the water tends to stagnate.

Pillar Point near Half Moon Bay also received poor grades, and was singled out as a "beach bummer."

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There's an upside to California's drought: Cleaner beaches