Heavy rains and humid air may be to blame for flourishing bacteria that has caused the closure of many Massachusetts beaches.
Beaches from Quincy to Wellfleet were off limits Thursday because of high bacteria counts in the water, and while heavy rain may be a factor in the increase in bacteria, no one is certain of the cause.
“This widespread closure is extremely unusual but may be attributable to either the heavy rains of the night before or windblown dead seaweed on our north shore, which may be fermenting and releasing bacteria during high tide cycles,” said Nantucket Health Department director Richard Ray.
“It could be many things, but we haven’t had a large rainfall like this in a while,” Ray said.
Rain and thunderstorms have been frequent across the state for the past few days — a range of 1 to 3 inches of rain fell in Cape Cod on Tuesday — and the rain is predicted to continue through the weekend.
The Massachusetts Department of Public Health requires weekly tests for the bacteria enterococci.
If the bacteria in collected water samples exceed state standards, the beach is closed for swimming.
Contaminated water poses some threat to swimmers, particularly if E. coli is present. Problems could include benign intestinal distress, but those with compromised immune systems or open wounds could have a more dangerous reaction, Ray said.
Among the closed beaches were East Beach, West Beach, and the beach inside Fort Taber Park in New Bedford, which were all closed Wednesday as a preventative measure after the heavy rainfalls.
All but a section of West Beach was reopened late Thursday afternoon, according to the New Bedford Health Department.
All four sections of Wollaston beaches in Quincy were closed Thursday due to high bacteria counts, with the highest levels at the Sachem Street section.
Along the Cape, Nauset Light Beach in Eastham and Marconi Beach in Wellfleet were closed Thursday.
Nantucket experienced the most beach closures Thursday, with 10 beaches affected by high bacteria counts: 40th Pole, Children’s Beach, Dionis Beach, Jetties Beach, Miacomet Beach, Sewerbeds Beach, Washing Pond, Washington Street, Cliffside Beach Club, and Wauwinet-Bayside Beach.
According to the town’s website, all beaches were allowed to reopen Thursday evening.
The remaining closed beaches will be reopened to swimming once water returns to acceptable quality levels.Sarah N. Mattero can be reached at firstname.lastname@example.org.