Ten beaches, from Quincy stretching down the South Shore, were closed Thursday due to high bacteria counts, including a Duxbury beach shut down after posting its highest count in more than five years.
After recent rains, several Quincy beaches had bacteria counts much too high for safe swimming. Back Beach, off Delano Avenue, was almost 60 times the recommended level, according to data from the state’s Bureau of Environmental Health.
Orchard Beach, Rhoda Street Beach, and four Wollaston beaches along Channing, Milton, and Sachem streets and Rice Road, all in Quincy, also were closed Thursday, according the Bureau of Environmental Health website.
“We closed the Wollaston beaches as a precautionary matter,” said Department of Conservation and Recreation spokeswoman S.J. Port. “We will retest tomorrow and see what the results shows. We hope that it is not anything of alarm.”
In Duxbury, the residents’ beach had 30 times the recommended level of bacteria, which is exceptionally high for that beach, said The Save the Harbor/Save the Bay spokesman Bruce Berman.
“It’s too early to tell if there is a problem,” Berman said. “We won’t know until the results of [Thursday’s] tests are released on Friday. If those come back high, then there may be something going on that needs to be addressed.”
Beaches are tested on a regular basis during warm weather months in order to ensure the water is safe for swimming. High levels of bacteria in the water are not uncommon after rain, especially within the first 24 hours.
More than an inch of rainfall was recorded in the past 10 days at of Logan Airport, the only area for which data was available, said Kevin Cadima, a meteorologist from the National Weather Service in Taunton.
Typically, beaches are tested for a bacteria called enterococci, an indicator of contamination found in intestines and fecal matter. Enterococci can cause upset stomachs, diarrhea, rashes, or earaches.
“High levels of enterococci at the beach indicate the waters may also contain other disease-causing microbes that are present in sewage but are more difficult to detect,” according to the Woods Hole Oceanographic Institution’s website.
As a result, beaches are closed if they have readings higher than 104 colony-forming units per 100 milliliters of water. At Quincy’s Back Beach, Wednesday’s count was the highest it has been in the past five years, with 6,015 units per 100 milliliters.
Berman said the high bacterial levels could be due to large amounts of bacteria building up in sewage pipes during dry spells that is then deposited into the water after it rains. Other explanations could be inaccurate tests or broken pipes.
“If the results come back normal on Friday, Duxbury and Delano may never know what caused the high levels,” Berman said.
Although the four beaches in Wollaston had lower bacterial counts, rain has prompted officials to close them as a precautionary measure.
Alejandra Matos can be reached at firstname.lastname@example.org. Follow her on Twitter @amatos12. Jessica Bartlett can be reached at email@example.com.