According to the Natural Resources Defense Council, there were more than 13,000 closures and advisories at ocean and freshwater beaches in the United States in 2001 - the vast majority prompted by lab tests showing elevated levels of fecal bacteria in the water.

But a recent study in the journal Environmental Science & Technology (ES&T) is raising questions about the reliability of water monitoring programs now in use at most U.S. beaches. The study also has uncovered a surprisingly strong correlation between beach pollution and the forces of nature - including rainfall, sunlight and the gravitational pull of the moon.

''There are many factors that can influence the concentration of bacteria in a sample of water,'' said Alexandria B. Boehm, the Clare Boothe Luce Assistant Professor of Civil and Environmental Engineering at Stanford and lead author of the ES&T study. After conducting extensive field studies of Southern California beaches, Boehm is extending her research to the sandy shores of Northern California not far from the Stanford campus.

''A lot of water sampling is done once a day, but there usually is a one- to four-day delay between the time a sample is taken and testing results are known,'' she explained. ''In our study, we found that a lot of pollution events last just one day or one hour, so the problem is likely to have passed by the time a warning sign is posted.''

The result, Boehm said, is that people may be barred from swimming at beaches that are actually clean, while contaminated beaches may be inadvertently kept open, exposing swimmers, snorkelers and surfers to a wide range of illnesses - some producing mild symptoms (such as chills, fevers and upset stomachs) and some that are potentially lethal (including hepatitis and meningitis). Beach closures also can have a serio
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Contact: Mark Shwartz
mshwartz@stanford.edu
650-723-9296
Stanford University
11-Nov-2002