The West Tisbury and Chilmark Boards of Health issued a cyanobacteria bloom advisory for several regions of Tisbury Great Pond after samples taken Wednesday came back positive for the potentially toxic algae.
The blooms were mostly isolated to the northern regions of the pond, while areas closer to the beach and main body of the pond showed low to no cyanobacteria presence. The boards of health, who issue advisories based on expert recommendations, advise against any recreational activities in the area as well as against fishing in Town Cove, Pear Tree/Muddy Cove, and Tiah’s Cove.
Detections were made by scientists at MV CYANO, a collaboration between Island boards of health and experts from the Great Pond Foundation to monitor cyanobacteria.
Cyanobacteria, also known as blue-green algae, are a type of microscopic photosynthetic, aquatic bacteria. They are responsible for a lot of the oxygen on Earth, but an overgrowth, or a bloom, has the potential to produce cyanotoxins that can cause adverse health effects in humans and animals upon contact or ingestion.
In the Tisbury Great Pond, the recent blooms are benthic, which means the “green clumpy cells are near the bottom of the pond, rather than on the surface, and the water column looks clear,” a press release from the Chilmark Board of Health said. This is different from more common blooms where there is a green scum on top of the water.
This is the third year in a row that after the great pond was cut that benthic algae was detected. The pond elevation goes down and the heads of the coves are exposed, and a bloom subsequently occurred for the last three seasons, said Emily Reddington, biologist and executive director of the Great Pond Foundation.
Advisories typically last two weeks as per guidelines laid out by the state Department of Public Health. But subsequent detections can prolong the advisory.
MV CYANO monitors nine ponds on the Island: Squibnocket Pond, Chilmark Pond, Tisbury Great Pond, Watcha Pond, Edgartown Great Pond, Cracktuxet Pond, Seth’s Pond, James Pond, and Mink Meadows Road. There was a detection June 23 in Mink Meadows, and Squibnocket Pond is still under an advisory after a follow-up detection.
In good news, Reddington said, Chilmark Pond is doing much better than last year.
