AMESBURY — Blue-green algae has struck Lake Attitash again, and residents are being urged to stay out of the water until the bloom of dangerous bacteria has abated.
The Lake Attitash Association announced yesterday that a recent water sample taken from the Merrimac State Boat Ramp contained dangerously high concentrations of cyanobacteria — more commonly known as blue-green algae — and the state has issued an advisory urging residents to avoid contact with the water for the time being.
Blue-green algae is known to produce toxins that can be harmful to humans and pets in high enough concentrations, and the frequent blooms on Lake Attitash have been a persistent thorn in the side of local residents and officials over the past few years.
Last summer was especially bad, as the state issued advisories in May, July and September that essentially kept boaters away for the whole season. The fact that this summer’s first advisory didn’t come until late June is encouraging, but association spokesman Ron Klodenski said it’s likely more of a reflection of the weather conditions we’ve had this year compared to last than anything else.
“I don’t know enough about it to judge that, but I’m guessing that the appearance of cyanobacteria might have more to do with the rain we’ve had lately, bringing in runoff and such,” Klodenski said. “But that’s an inexpert opinion.”
The state has three criteria to determine if dangerous concentrations of cyanobacteria are present in a body of water. One is if a water sample contains over 70,000 cyanobacteria cells per milliliter, another is if the water contains microcystin toxins above 14 parts per billion and the last is if visible patches of scum can be seen on the water.
The water sample taken this week found 79,000 cyanobacteria cells per milliliter, which exceeds the state guideline and prompted the advisory. In order for the advisory to be lifted, two consecutive tests must show results below the state guidelines in all three categories.