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.
The tests are administered weekly, which means that the earliest the advisory can be lifted is July 4.
Klodenski has said that the blue-green algae blooms are caused by an overabundance of phosphorous in the water, and over the past year the Environmental Protection Agency has been conducting a study of the lake to try to pinpoint the exact source.
The results of that study have yet to be released, and depending on the findings, the association plans to take measures to combat the problem and hopefully rid the lake of the microscopic pest once and for all.
“When we get that information then maybe we can be more active in combating the problem,” Klodenski said. “Where right now we’ve done all we can do because we need more data to decide what to do next.”
Those results could come within the next couple of weeks, Klodenski said.
Although phosphorous is believed to contribute to the explosive growth of the bacteria, blooms can form in the water at any time, particularly in warm, slow-moving waters that are rich in nutrients such as fertilizer runoff or septic tank overflows, the Centers for Disease Control said.
Trying to predict how the bacteria will behave in the future is difficult because its growth is impacted by factors like currents, temperature and the amount of sunlight.
Lake Attitash does remain open when a state health advisory is in place, so residents and boaters can still go out on the water if they choose to. Klodenski said he has seen people out on the water while an advisory is in place, saying his guess is a lot of people don’t pay attention to it.
“But as far as the association is concerned, they should,” Klodenski said. “I think it may be more of a risk for small children and pets, because they’re more likely to swallow water and ingest it.”