A study sponsored by the Great Pond Foundation aimed at monitoring the presence of cyanobacteria in Vineyard waters has shed light on which ponds experienced the highest density of toxic blooms over the past few years.
In the last year, at least two ponds have been found to contain cyanobacterial toxins, prompting boards of health to issue an advisory.
Cyanobacteria, or blue-green algae, are a group of photosynthetic microorganisms that are among the Earth’s oldest, and are found all over the world, including in Vineyard waters.
They help generate oxygen in the atmosphere, and are one of the most diverse and abundant organisms on the planet. Most cyanobacteria cause no harm, but a few can grow rapidly, or bloom, and produce toxins. When in higher concentrations, the blooms can cause adverse health effects in humans, pets, or livestock who wade in or ingest the water.
First launched in 2021, MV Cyano is a collaborative initiative between Island health agents and the Great Pond Foundation (GPF) to actively monitor the prevalence of cyanobacteria. Through color-coded signage, Island health officials hope to better educate the public about the potential dangers of cyanobacteria blooms, and offer information on the status of each pond.
That colored signage is associated with the level of risk in a particular pond, from green to red.
At a presentation Thursday, GPF scientists revealed findings from the past two years of data collection.
The samples are tested mainly for microcystin toxins, GPF scientific program coordinator Julie Pringle said. MV Cyano does not routinely test for other cyanotoxins.
Out of all the ponds tested, only samples from Chilmark Pond and James Pond revealed presence of microcystin toxins.
All Vineyard waters sampled also fall below the safety threshold recommended by the U.S. Environmental Protection Agency for swimming.
Chilmark Pond saw highly dense blooms in the western part of the pond, where salinity levels are lower. In that pond, water moves from west to east, and is then flushed out by ocean water.
Samplings from two blooms in Chilmark Pond west, in the middle and end of the summer, revealed the presence of microcystin toxins, but remained under the threshold for drinking water laid out by the EPA.
Edgartown Great Pond saw a higher density of cyanobacteria last year than it did before, Pringle said. However, it remained mostly in the yellow risk category. When tested, no microcystins were detected.
Similarly, Crackatuxet Pond saw a significant increase in cyanobacteria, including a two-month bloom, in 2022, compared with 2021. Although that pond was temporarily upgraded to red risk, no microcystins were detected.
Watcha Pond and Tisbury Great Pond remained mostly in the green and yellow risk categories, with far less cyanobacteria presence.
Sengekontacket showed barely any cyanobacteria growth, remaining in the green risk category throughout 2022.
Overall, 2022 had more cyanobacteria growths than in 2021, Pringle said.
MV Cyano reps offered tips on how to visually identify the presence of cyanobacteria, in order to avoid contact.
Often, ponds turn an opaque shade of green as a result of overgrowths of cyanobacteria. Those blooms are especially common in fresh waters that have been polluted by nitrogenous waste.
According to the U.S. Environmental Protection Agency (EPA), there are a number of factors that contribute to the formation of cyanobacterial blooms, including water temperature, light, changes in pH levels, nitrogen and phosphorus loading, trace metals, and alteration of water flow.
Cyanobacteria is buoyant, follows the movement of the water, and can be pushed by the wind. Therefore, blooms tend to accumulate at shorelines, Pringle said.
But, she said, the winds can shift, and “the location of a bloom can change from one day to the next, or really one hour to the next.”
Cyanobacteria blooms can vary in color and shape, from bright green to blue-green, and patchy to more dense. Those conditions can change rapidly.
Scientists warn against consuming marine life from waters that are actively experiencing dense concentrations of cyanobacteria, since fish and shellfish can accumulate biotoxins that can be dangerous to ingest. “Like any living system, there’s life in it,” GPF Executive Director Emily Reddington said following the presentation. “We like living systems and ecosystems because they’re more resilient to change; they can respond.”
But Reddington advised exercising caution when in contact with the blooms, and offered a reminder. “We’re not going into swimming pools when we go into these great ponds,” she said. With life come bacteria, phytoplankton, small parasites. “It’s the same thing with the ocean. It’s not sterile,” she said.
Blooms can be reported to MV Cyano at mvcyano@greatpondfoundation.org.