This section of the website gives an overview of all the ponds and watersheds on the Island. For more detail about coastal ponds, go to the Coastal Ponds section of the website.
The 98 fresh and coastal ponds of the Vineyard are fed by seepage from the aquifer, as well as by runoff from the surrounding uplands and by direct precipitation within the pond’s watershed, the area of land that contributes water to a pond. The salinity in the coastal ponds is reduced by the fresh water input creating specialized habitat and giving these ponds their unique, estuarine nature. An estuary is an enclosed body of water that has an open connection to the sea and is measurably diluted by fresh water from the surrounding land. The fresh ponds rise and fall in a pattern that is a close parallel to the water table changes indicating that they are fed by groundwater. The slope of the surrounding upland determines the area that contributes surface runoff to a pond. The shape of the water table around a pond determines the direction that water within the aquifer flows and the ultimate area that will contribute groundwater to a pond.
In the western, hilly areas of the Vineyard, the soil is developed on impervious clay and till. Seepage through this kind of soil is very slow and aquifers may be confined to pockets or beds of sandy material. In these situations, the watershed of a pond like Menemsha Pond, James Pond or Daggett's Pond is defined by the topography that directs the flow of surface runoff to the pond.
The south shore and the north shores east of Tashmoo have very sandy soil and the watershed is not determined so much by the topography of the surrounding upland but rather by the groundwater flow paths. The Commission has prepared a Watershed Map illustrating the approximate groundwater contribution areas to the coastal ponds.
These watersheds define areas where pollutants entering the ground may eventually affect coastal pond water quality. Nitrogen from wastewater disposal, fertilization of landscapes and farm fields and stormwater runoff is the primary nutrient of concern. The watershed map is the starting point for determining the impact on water quality of buildout within each pond's watershed.
Freshwater Ponds: There are 61 fresh water ponds in the six Vineyard towns that total about 615 acres in area.
Coastal Ponds: See the Coastal Ponds section of this website.