AMESBURY – The most recent bloom of blue-green algae on Lake Attitash has run its course, and state officials are now giving residents the go ahead to return to the water.
The Lake Attitash Association announced that a water sample taken from the Merrimac State Boat Ramp contained a safe concentration of the dangerous bacteria for the second week in a row. As a result, the state advisory urging residents to stay out of the water has been lifted.
Blue-green algae, which is known scientifically as cyanobacteria, is known to produce toxins that can be harmful to humans and pets in high enough concentrations. When a state advisory is in place, people are urged to stay away from the water and especially to avoid ingesting it.
Lake Attitash has been prone to blue-green algae blooms, particularly over the past few summers, and the Environmental Protection Agency is currently in the process of completing a study that would explain where the algae comes from and how it can be combated. The Lake Attitash Association is expecting the results of that study later this summer.
In order to detect algae blooms in the lake, officials take weekly water samples at the Merrimac State Boat Ramp, and there are three criteria that could trigger an advisory if met.
One is if the water sample contains more than 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 latest advisory was triggered on June 17 when a water sample contained 79,000 cyanobacteria cells per milliliter, above the state guideline. In order for an advisory to be lifted, two consecutive tests must show results below the state guidelines in all three categories.
Last week, the sample barely checked in under the state guideline, as the sample contained 69,000 cells per milliliter. This week saw a significant reduction in blue-green algae concentration, however, as Monday’s sample contained only 44,000 cells per milliliter. There was no visible scum or high toxin readings in either case, allowing the advisory to be lifted just in time for the Fourth of July.
While an advisory doesn’t prompt a closure of the lake, Lake Attitash Association officials urge residents to obey the advisory and stay out of the water when blue-green algae blooms are present in the water.
According to the state Department of Public Health, exposure to high concentrations of cyanobacteria can cause skin, eye and ear irritations, and occasionally respiratory and gastro-intestinal illnesses as well.