California Beach Safety - Beaches

Avoid Beach Waters after the New Moon

Avoid Swimming in the Pacific Ocean after it rains.

Beach germs, tides linked
New study points to an odd lunar pattern in ocean contamination.

People worried about exposure to bacteria might want to avoid swimming in the ocean during new or full moons, according to a new study.

The study, of 60 beaches from Point Zuma to Corona del Mar, showed that counts of one type of bacteria associated with human sewage rise at certain times during the lunar cycle. And so far, no one knows why.

The effect was noted in 2002 at Huntington Beach by Alexandria Boehm, a Stanford University environmental engineer.

Boehm wondered if it was a peculiarity of Huntington Beach or something more widespread. So she analyzed ocean-water sampling data up and down the coast, and found that almost all showed the same pattern.

The tides that occur during new or full moons are known as spring tides, when high and low tides are at their extremes. (The term has nothing to do with the season.)

"My friends ask me – 'cause I study dirty beaches – 'When should I go to the beach?'" Boehm said Friday. "I say, if you're worried about it, I wouldn't go to the beach during spring tides."

The effect was strongest, she said, when the tide was ebbing during a spring tide.

Monica Mazur, a senior environmental-health specialist at the Orange County Health Care Agency, said others have been noticing that effect since at least 1999. But she believes it is often too small an effect to be useful for regulation of beaches, such as by issuing warnings about bacteria.

The bacteria, enterococcus, is one of three measured by regulators to determine whether human sewage is present in a water sample. But it can also be found in decaying plants and the feces of animals, including birds.

Another possible source, said Boehm: polluted groundwater just beneath the surface near the coast.

For now, experts say, the finding is an interesting result that will require further research. Boehm's study, which she worked on with the Southern California Coastal Water Research Project in Westminster, appears in the Aug. 1 issue of Environmental Science & Technology, a journal published by the American Chemical Society.