Blooms of toxic algae close swimming holes
It varies between chartreuse and turquoise, smells rotten and is responsible for spoiling summer fun for countless children and swimmers across Greater Boston.
The culprit? Blue-green algae, which has invaded swimming holes in Newton, North Andover, Winchester, Halifax, and elsewhere, raising concerns about public health and forcing officials to close some of the ponds.
According to the state’s Department of Public Health, nine ponds were under a blue-green algae advisory last week. Communities warned swimmers to stay away and residents to keep their pets out of the water.
Some algae blooms can produce toxins that cause skin and eye irritation, trigger asthma-like symptoms, and, if swallowed in large amounts, harm the liver.
Massachusetts has seen a rise in the number of blue-green algae blooms in recent years, said Suzanne Condon, director of the state agency’s Bureau of Environmental Health.
“We’ve seen a slow, steady increase,” Condon said.
Test results indicated six lakes and ponds had elevated levels of blue-green algae around the first week of August in 2009, compared with the nine last week.
Newton closed Crystal Lake, near Newton Centre, indefinitely last week for the first time in recent memory because of elevated bacteria levels. The city canceled the latest round of swim classes at the lake and offered families a refund.
“It’s sad to see it quieted so early in the season,” said Linda Walsh, the city’s director of health and human services.
In North Andover, blue-green algae was to blame, for the first time, when Stevens Pond was closed last month. The pond hasn’t reopened.
“It’s very unusual,” said Susan Sawyer, North Andover’s health director. “We had no history with it.”
The town initially sent water samples for a weekly E. coli bacteria test, when the lab noted higher than usual levels of cyanobacteria, or blue-green algae, Sawyer said.
When she went to the pond to check it out, Sawyer said, she was surprised by the murkiness of the water and the rotten smell.
“It was pretty bad,” she said.
State health officials have been monitoring Stevens Pond and advising the town, which is new to blue-green algae problems, on whether to keep it closed, Sawyer said. The pond has been closed in past years because of other bacteria issues.
“We hope that this will be an unusual year and we won’t have to deal with this next year,” Sawyer said. “But we’ve learned a lot.”
Blue-green algae blooms are triggered by nutrients — such as those found in fertilizers, leaking septic or sewer systems, and animal waste — and by warm temperatures.
This year’s mild winter and hot summer likely caused more ponds to experience the blooms, and earlier in the season than usual, Condon said.
Other bodies of water under advisories last week included Lovell’s Pond in Barnstable, Moll’s Pond in Eastham, Santuit Pond in Mashpee, Walker’s Pond in Brewster, and Wedge Pond in Winchester. Swimming has been prohibited in several, including Wedge Pond and Lovell’s Pond.Other local bodies of water under advisories last week included Wedge Pond in Winchester, and on Cape Cod, Lovell’s Pond in Barnstable, Moll’s Pond in Eastham, Santuit Pond in Mashpee, and Walker’s Pond in Brewster. Swimming has been prohibited in several, including Wedge Pond and Lovell’s Pond.
State officials have received a federal grant to further study blue-green algae, and are monitoring five bodies of water, including West Monponsett Pond in Halifax, with historically high bacteria levels. The research may help give officials more insight into why more ponds and lakes are experiencing blue-green algae, Condon said.
For now, Massachusetts recommends that if bacteria levels in the water exceed the state’s safety threshold of 70,000 cells per milliliter of water, communities post advisories. It is up to each community to determine whether to close the pond or lake, said Anne Roach, spokeswoman for the Department of Public Health.
For example, Woburn posted signs around Horn Pond warning of the elevated bacteria counts. Swimming is prohibited at the pond at all times, so the advisories serve as a warning for pet owners to keep their dogs out of the water and fishermen to be careful, said John Fralick Jr., the city’s health agent.
In some communities, the advisories have likely put an early end to the swimming season, which closes around the third week of August. The state requires two consecutive weeks of clean water samples before an advisory is lifted and swimmers and pets can return to the water.
That’s because even as an algae bloom breaks up it can release toxins that can be harmful, Condon said.
Swimming at Crystal Lake is unlikely for the remainder of this season, Walsh said.
Newton is waiting for the latest water sample results, but Walsh said when she stopped by Crystal Lake earlier this week, it was a lime-green color, indicating that the algae was still present.
“It was definitely an abbreviated season,” she said.
Deirdre Fernandes can be reached at deirdre.fernandes@com.