Why dredging matters, EGP delisted, Watershed Density

"The water that divides us from the mainland, unites us as a community. Martha’s Vineyard is celebrated for abundant and beautiful natural spaces, but one of our greatest assets is our strong and resilient community. Our physical isolation from the mainland reminds us of the essential role our community and its resources play in our ability to respond in times of crisis."

Emily Reddington | Executive Director

-excerpt from Gazette Commentary

Dredging is Essential to Pond Health

A decade of dredging in Edgartown Great Pond has increased the circulation of seawater throughout the Pond during openings, resulting in measurable improvements to water quality and ecosystem health. With regular dredging, seawater from the Atlantic Ocean reaches all corners and coves of the Pond.

Following a winter without dredging, seawater did not reach pond coves during the May 2020 cut.

Salinity (white box) is shown in parts per thousand (ppt), with the change after the cut indicated in blue. Good pond flushes cause salinity to increase pond-wide 8-12 ppt. The spring cut, following a winter without dredging, did not flush the pond adequately.

A Tale of Two Cuts

Successful openings of the Pond occur when the volume of Pond water exchanged with seawater is maximized such that the salinity increases pond-wide. Data from 2019, following a decade of regular dredging when conditions are ideal, indicate EGP needs to be open a minimum of 9-11 days to flush all regions of the Pond and maximize salinity. In 2020, following a year when winter dredging was skipped (2019/2020), the circulation within the Pond decreased and the flushing of the pond was inadequate to support pond optimal health....

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EGP Delisted by DEP

Edgartown Great Pond has been delisted by the Massachusetts Department of Environmental Protection (Mass DEP). This means that Edgartown Great Pond has sufficiently low levels of bacteria to be considered safe for shellfishing, swimming, and boating.

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Watershed Housing Density

One of the reasons Edgartown Great Pond is among the healthiest Island ponds is because of the very low housing density immediately surrounding it. Properties with frontage on the pond have an average housing density of 212 square feet per acre (367,049 ft² / 1734 acres).

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