EagleTribune.com, North Andover, MA

Merrimack Valley

January 31, 2013

Town rallies to bring swimming back to Stevens Pond this summer

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.

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