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Another Mass. lake falls victim to cyanobacteria, and 2 ocean beaches close over high bacteria counts

A Sharon lake and two Winthrop beaches are now off limits.

A cyanobacteria algae bloom in the Charles River in June 2012. John Tlumacki/Globe staff

A lake in Sharon closed this week due to a suspected cyanobacteria algae bloom while two ocean beaches in Winthrop were placed off limits because of high enterococci levels.

Sharon officials shut down access to Lake Massapoag after a “visible suspected cyanobacteria scum” was discovered and reported to the Massachusetts Environmental Toxicology program, according to a statement released Thursday.

Residents who came in contact with the lake water were advised to rinse off at home as soon as possible.

The lake will be closed until the Massachusetts Department of Public Health determines it is safe to enter again.

The announcement came on the heels of the closure of Lake Cochituate — which spans portions of Framingham, Natick, and Wayland — on Wednesday after a cyanobacteria bloom was detected.

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Cyanobacteria, also known as blue-green algae, can produce cyantoxins, which are “among the most powerful natural poisons known,” according to the U.S. Centers for Disease Control and Prevention.

The deaths of several dogs who came in contact with the bacteria made national headlines in 2019.

“They can make people, their pets, and other animals sick,” the CDC says. “Unfortunately, there are no remedies to counteract the effects.”

In Winthrop, Pico Beach and Donovans Beach closed on Thursday after the town’s weekly water quality test yielded high levels of enterococci, “which is an indicator of fecal pollution and possible enteric pathogens,” officials said in a statement.

Enterococci can cause infections, the CDC says. The bacteria are also “constantly finding new ways to avoid the effects of the antibiotics used to treat the infections they cause,” the agency says.

Winthrop officials say higher levels in the water are usually brought on by heavy rainfall, which Massachusetts has seen plenty of this month. Normal levels typically return after the water is retested, they said.

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