After more than two years without a blade of eelgrass in sight, the aquatic vegetation in Edgartown Great Pond is starting to rebound, giving Islanders hope that the coastal waterbody can stand resilient against mounting pressures.
Eelgrass, the green, quarter-inch wide sea plant that was once found widely in Vineyard ponds, has been disappearing in recent years. A keystone species, the eelgrass provides oxygen-rich habitat for shellfish and other creatures, but has been threatened by warmer temperatures in ponds, increased nitrogen and low salinity levels.
Edgartown Great Pond, one of the largest great ponds on the Island, had thriving eelgrass beds and clear water conditions in 2018. In the years following, the plants started to thin out and the water became more turbid. By 2022, hundreds of acres of eelgrass had died and there were none to be found in 2023.
Researchers were pleased last summer when they found patches of eelgrass had returned to areas such as Lyle’s Bay, a harbinger of healthy levels in the pond that conservationists hope continues into 2026.
“We didn’t find eelgrass until June 2025,” said Emily Reddington, the president of the Great Pond Foundation, a nonprofit that works to protect the Island’s coastal ponds. “It was a tangible sign of hope.”
A 900-acre large pond along the south shore, with a small barrier beach between it and the ocean, Edgartown Great Pond is a popular spot on the Island, and once the home to a thriving shellfishery.
With its popularity, though, has come an increase in development nearby, which is believed to add to the amount of nitrogen in the pond. Nitrogen, the main culprit of degradation in many Vineyard ponds, can come from a variety of sources, but is largely attributed to wastewater and runoff from nearby homes. That nitrogen can fuel algal blooms and can choke out the eelgrass.
Eventually, cyanobacteria blooms can prove dangerous for animals and humans alike.
“At that point, it’s not safe to interact with the body of water,” Ms. Reddington said. “Imbalance or impairment can be stinky and not pretty, but it can also be toxic.”
Efforts by the town to cut down the amount of nitrogen in the pond have proved successful, but the recent dip in health shows how fragile these ecosystems can be.
Rob Morrison, the town’s shellfish constable, said recent infrastructure upgrades have proved important in keeping the pond healthy.
“The number one thing that the town has contributed has been the wastewater treatment plant,” he said. “The first rebound, you can track with the upgrade of the wastewater treatment plant.”
The town also “cuts” the pond by digging a trench in the barrier beach that separates the pond from the ocean. Doing this allows the fresh, cold and salty ocean water to flush into the pond, and allows the growing nutrients that feed algal blooms to flush out.
Improvements in 2024 water quality were largely due to an 11-day opening in that July, preventing a late summer bloom that was seen in each two years prior. But recent years’ cuts have been open for shorter windows, raising concerns about options to flush out the water bodies.
For instance, the pond had been open for 92 days in 2018, and 78 days in 2019. In 2022, it was open just 15 days, and hasn’t surpassed 35 days since, despite multiple cuts per year.
Successful cuts are the result of a number of natural factors, including water-levels, rainfall and tides. Some of the more successful exchanges have come after large rainfalls and iced-in winters when the water levels were high.
This year, though, a cut was open from March 19 until April 7, for a total of 19 days, surpassing all of 2025 and putting the pond in a great position to start the year.
“This has been a great cut,” said Owen Porterfield, the scientific program manager at the Great Pond Foundation. “We’re hoping that we are kind of building off that resurgence last year.”
Cleaning the pond up could help more shellfish thrive there, which in turn helps improve water quality. Emma Green-Beach, the executive director at the Martha’s Vineyard Shellfish Group, has done surveys in the pond and remembers years where the eelgrass was so thick, it could be hard to find spots for oysters.
But the forest of vegetation was weeded out as algal blooms spread. It got to the point where she would feel emotional over each individual blade she came across.
“When you would find a piece [of eelgrass] on the beach, it’s sad,” she said. “You want to ask it a question: Where did you come from, are there more of you?”
The potential for nitrogen to seep into the pond has become a hot topic in recent months, as new housing proposals have come up at the Martha’s Vineyard Commission. The Great Pond Foundation and Vineyard Conservation Society have pushed back against these proposals, saying they could hurt the pond just as it’s getting its legs back under itself.
Their fear is that if more and more nitrogen is pushed into the pond, the relief measures, such as the cuts, won’t be able to keep up.
“Ultimately, to keep a pond healthy, you have to reduce the nitrogen input in the watershed overall,” Ms. Reddington said. “The good news here is there is tons of life in the pond….We want to cultivate this resilience.”
Ms. Green-Beach echoed the sentiment, saying this is an issue that needs to be constantly tended.
“We have to continue to work hard for the ponds,” she said. “One of these days it’s not going to come back if we are not staying vigilant.”
This article appears in April 24, 2026.