Cyanobacteria bloom found in Chilmark

This is the first ‘red’ status cyanobacteria bloom of the summer season.

Middle Pond in Chilmark experienced a cyanobacteria bloom, and MV Cyano is keeping eye on other parts of Chilmark Pond as well. — MV Times

Middle Pond (a part of Chilmark Pond) in Chilmark was marked as a red zone, or with a harmful cyanobacteria (a.k.a. blue-green algae) bloom advisory, by MV Cyano, a “collaborative initiative among Island boards of health and scientists from Great Pond Foundation.” The Chilmark board of health issued an advisory for portions of Chilmark Pond, including Middle Pond and Doctor’s Creek, after this revelation. 

Chilmark health inspector Marina Lent said this is the first cyanobacteria bloom of the summer. Lent told The Times people should stay out of the water, especially children and dogs who may ingest the water accidentally, in orange, or “watch,” status areas. Cyanobacteria blooms have the potential to kill dogs and make humans sick. She also warned against people with vulnerable body parts, like sores, from coming in contact with the water. Even healthy people, Lent said, should rinse off as soon as possible once on shore. However, it is only safe on boats in red zones.

According to MV Cyano, data on the pond was collected on July 20 and 21, based on reports of “green pools observed by two members of the pond community,” and the staff members of the foundation conducted an analysis of the water samples collected. Since cyanobacteria blooms can spread rapidly, the connected Lower Pond has been placed under a cyanobacteria watch status. No further data is available on Upper Pond. 

“Great Pond Foundation, we have a contract with them to do the testing, went out and collected samples in the scum area. And it was also windy,” Lent said. “[The wind] had driven all of the surface scum into those little pockets, so it did collect very dramatically, very visible.”

Lent said the tested water sample was “very high for cyanobacteria.”

“It also showed there were no more green algae whatsoever. In other words, the blue-green algae outcompeted all other algal species,” Lent said. “Normally, they’re in balance with each other.” 

The foundation used fluorometry, or the measurement of emitted fluorescent light, to determine cyanobacteria levels. The foundation’s executive director Emily Reddington told The Times the samples have been sent to Stony Brook University’s Gobler Laboratory. 

“Once samples are in the orange or red tier of MV Cyano, samples are sent for cyanotoxin analysis with Dr. [Christopher] Gobler’s [lab],” Reddington said. 

Since the movement of water and wind can spread cyanobacteria blooms, the entirety of Middle Pond was labeled as a red zone for precautionary measures. Lent said a follow-up on the scum area is planned. 

“The part we normally sample was still in the orange category … it wasn’t red yet, but we decided the entire Middle Pond be designated red because of the intensity of that bloom; we have not seen those levels even last year in Squibnocket when there was a bloom,” Lent said. 

“We’re trying to strike a balance between restrictions and risk, people assessing their own risk.” 

Cyanobacteria blooms usually occur in freshwater, so the blooms occurring on the Island’s brackish ponds make them an area of research. Additionally, Lent said, the increase in population and the hot weather make the conditions for blooms to occur more likely. 

Currently, the foundation conducts weekly tests at the ponds. 

“We should be looking at what states to the south of us experience in their waters, and start preparing for similar things to look out for,” Lent said, listing New Jersey and Maryland as states that also have tidal and coastal ponds.

Most parts of pond maps on MV Cyano’s website show primarily yellow, or alerts, for cyanobacteria, but there are still two other locations that have the orange status: James Pond in West Tisbury and Squibnocket Pond’s Chilmark segment. For those who see “green scum” outside the red zones, MV Cyano recommends not to have contact with the water, and to email them at


  1. Cyanobacteria is typically caused by nitrogen coming from sources such as fertilizer runoff and/or septic systems. So I have an idea. Why don’t we impose a real estate transfer tax on Vineyard homeowners so we can make it easier for more people to live here?

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