Small drain pipes carrying runoff from Newport Beach streets could be causing high fecal bacteria counts frequently detected in bay waters at so-called "baby beaches," according to a UC Irvine study.

Bays often are home to baby beaches because the water tends to be still enough for even the smallest swimmers. But that also makes them more likely to hang onto bacteria, experts say.

For years, experts have warned swimmers to steer clear of coastal waters during rainstorms because of increasing levels of bacteria carried from storm-drain runoff to bay and beach waters. However, a recent study by Newport Beach officials and UC Irvine researchers shows that runoff, dubbed by experts as "urban slobber," can make its way to enclosed bay beaches during dry seasons as well. The study was published last week.

The National Resources Defense Council's annual beach report card in 2013 showed that the majority of Newport's beaches bay and ocean did not often exceed bacteria levels considered acceptable by the U.S. Environmental Protection Agency. The beach on 38th Street did not exceed the bacteria levels at all in the 50 samples collected.

However, bacteria levels at the Newport Boulevard bridge at Newport Bay exceeded the standards 44% of the time one of the worst rates in California. Other areas of the bay tested considerably better, the nonprofit's report card showed.

"We were trying to determine why water quality can sometimes show elevated concentrations of bacteria on the shoreline, the area that impacts beachgoers directly," said Megan Rippy, a UCI postdoctoral urban ecologist.

Researchers found that runoff from watering lawns collects in the narrow pipes, gathering animal waste, fertilizer, oil and gas drippings from cars and other pollutants and becomes trapped in the pipes during high tide. The pollutants are then released in a pulse at low tide when storm-drain openings are exposed.

"Urban slobber is any runoff that runs onto our roads that haven't seen rain for a long time," Rippy said. "Whatever is in that runoff is delivered in a highly concentrated form by our storm system to our water bodies."

City engineers and researchers dyed waste that came out of pipes in the upper and lower portions of Newport Bay. They tracked the green plumes to determine how long the pollutants were present and where the waste migrated around the bay from 2006 to 2009.

Researchers found that since water in enclosed bays is generally calmer than at ocean beaches, the bacteria isn't diluted as quickly. Winds often force the runoff against the shoreline, where the water is shallow and swimmers and waders generally congregate, the study shows.

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Study links small drain pipes to pollution at Newport's 'baby beaches'