By Paul Tennant
---- — NORTH ANDOVER — Kathleen Lyons Stagno grew up with Stevens Pond.
Back in the 1980s, she often swam in the pond and ended up working there as a lifeguard.
“It’s been such a fixture,” said Stagno, who was among at least a couple of dozen residents who attended last night’s informational meeting at Town Hall on how to keep cyanobacteria out of the pond.
“Nobody will ever let it die,” added Stagno. She was accompanied by her 2-1/2-month-old daughter, Molly — who will likely be headed for the pond this summer if the town can win the war against cyanobacteria, also known as blue/green algae.
The pond, located near the lower end of Lake Cochichewick, the town’s drinking water supply, was closed to swimmers for most of last summer when large blooms of cyanobacteria appeared. Exposure to these microorganisms can cause humans to suffer rashes.
Keith Gazaille and Erika Haug, biologists with Aquatic Control Technology, a firm that advises the town on water quality, said the cyanobacteria can be driven away by several measures, including:
The application of chemicals, such as copper and aluminum sulfate, commonly known as alum;
flushing the pond;
use of ultrasonic frequencies, which disrupt the cell structure of cyanobacteria;
placing barley straw into the water, the decomposition of which releases a substance that helps get rid of cyanobacteria.
Haug said the survey of the pond she and Gazaille did Oct. 4 showed a higher than normal presence of phosphorus, which encourages the growth of cyanobacteria. Gazaille said a low dose of alum can reduce the level of phosphorus in a pond or lake.
Aquatic Control Technology achieved success with this method at a pond in Pembroke, he said.
Blake Martin, an engineer with Weston & Sampson, which did a hydraulic analysis of the pond, recommended against flushing.
“You’re losing too much water,” he said. “It’s not a viable option.” Public Works Director Bruce Thibodeau said the town has never flushed out Stevens Pond.
William Gordon, chairman of the Board of Selectmen, said Thibodeau and Aquatic Control Technology will craft a recommendation on how to rid the pond of cyanobacteria. The selectmen will then decide whether to adopt it, he explained.
Town Manager Andrew Maylor said he has recommended that $25,000 for cyanobacteria eradication be included in the public works budget.
Until last July, there were no recent invasions of cyanobacteria at Stevens Pond, Thibodeau noted. Longtime North Andover resident James Lafond, however, said that the pond has experienced water quality challenges.
Back in the 1970s, he recalled, the town removed truckloads of weeds and algae from the pond.
Like Stagno, Gordon did a lot of swimming at Stevens Pond during his growing-up years. He’s now the father of four young daughters who have all experienced the pond and he said he’s confident residents will be able to swim there again.