Oak Bluffs health agent Shirley Fauteaux closed the beach in Madeiras Cove, near the Sailing Camp in Lagoon Pond on Tuesday, after a water sample showed higher than allowable bacteria counts.
A sample taken during routine testing Monday showed 278 colonies of enterococci bacteria. Under state regulations, a beach must be closed to swimmers if the count exceeds 104 colonies per 100 milliliters of water.
Enterococci is a bacteria that signals the presence of other dangerous bacteria is in the water.
Ms. Fauteaux said she will test the water again on Wednesday, and if the results are within acceptable limits, she will reopen Madeiras Cove on Thursday.
The Massachusetts Bureau of Environmental Health advises that swimming in polluted water can cause gastrointestinal symptoms such as nausea, vomiting, diarrhea, and abdominal pain, respiratory symptoms such as sore throat, cough, runny nose, and sneezing, eye and ear symptoms including irritation, earache, and itchiness, dermatological symptoms like skin rash and itching, and flu-like symptoms such as fever and chills.
Most of these symptoms are minor most of the time, but they can occasionally be more serious, especially in sensitive populations such as those with weakened immune systems, children, and the elderly.