AMESBURY — Health officials are advising people to take caution around Lake Attitash this weekend due to high counts of a toxic algae.
The advisory, which falls short of a full closure of beaches on the region's largest lake, was issued after a Department of Public Health test showed high levels of cyanobacteria, which, if it blooms, appears as a blue-green slick on the water.
Though the beaches at Lake Attitash aren't officially closed, interim Health Agent Jack Morris said he wouldn't recommend going in the water until the bacteria levels have subsided.
"If I saw an advisory, I'd consider it a closure," Morris said yesterday afternoon. "Definitely don't let animals ingest the water or let young people come in contact or ingest it."
Lake Attitash beaches initially were slated for closure yesterday when the state Department of Public Health notified Merrimac and Amesbury of a potential bloom of cyanobacteria.
According to the DPH, a University of New Hampshire professor on a field study trip measured an average cell count of 140,000 cells per milliliter from the lake, double the amount considered safe. DPH collected two lake water samples on Thursday morning. They came back yesterday at 60,000 and 55,000 cells per milliliter, still high but under the threshold of 70,000 that would prompt a more strict ban on the water.
Fearing Lake Gardner could be affected, the town initially posted an advisory for that lake as well, but it has since rescinded it and said the town's public beach is safe for swimming.
Morris said the advisory at Lake Attitash will continue through the weekend, and the lake will be retested on Monday.
"There's obviously a concern because the levels are elevated," he said. "It's going to be sunny and warm (today). It's perfect conditions for an algae bloom."
According to the Center for Disease Control, cyanobacteria is found in both oceans and fresh water. Aquatic cyanobacteria are probably best known for the extensive and highly visible blooms that can form in both freshwater and the marine environment and can have the appearance of blue-green paint or scum.
The association of toxicity with the algae has frequently led to the closure of recreational waters when blooms are observed.
"The algae is naturally occurring, but with the rain and runoff, the bad weather has made it worse," Morris said. "The nutrients added to the water have made the algae explode."
Yesterday, signs could be seen at Lake Attitash warning swimmers of the algae's dangers. Pictures of murky green waters illustrated what swimmers should avoid.
"Algae is capable of producing toxins that can be dangerous to humans and pets," the signs state. "People and pets should avoid contact in areas of algae concentration, even on shore. Do not swallow water, and rinse after contact."
DPH spokesman John Jacob said based on visual observations, there is an algal bloom present.
"Our general guidance is to limit exposure to water at levels of 70,000 cells per milliliter of water or higher," Jacob said. "Local health (officials) posted warning signs on the beaches based on that information. The decision to close beaches is a local one."
Jacob said the algae bloom requires sunlight to survive, and it is going to take a change in weather for local beaches to be safe once again.
" A change in weather (cloudy days, rain, wind) or nutrients (fewer entering the water body and available) can lead to less algae," Jacob said. "Limiting exposure to the algae limits health impacts."
The DPH said yesterday, once sample testing is complete, they will be working with Amesbury and Merrimac to address the matter and determine the next steps to protect public safety.
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