With no natural opening to the sea, the barrier beach along the south shore of Chilmark Pond has been intentionally breached to the Atlantic Ocean for hundreds, if not thousands of years. The Wampanoag people began the practice to allow fish to spawn in the brackish pond waters and maintain the shellfishery. Since the 1600s, Chilmarkers have sustained this practice which in addition to supporting the fishery (as recently as the 1960s, the Pond supported a commercial fishery) also protect the Pond’s ecological health and controls flooding of the surrounding marshes and homes.

Chilmark Pond openings are now managed by the Chilmark Pond Association, operating under the authority of the 1904 Act to Provide for the Drainage of the Lowlands and Meadows around certain Great Ponds in the County of Dukes County.

Excessive nutrients (nitrogen and phosphorus) are the greatest ecological threat to Chilmark Pond. This pollution load, coupled with extended summer droughts and heat, creates ideal conditions for excessive growth (plant/algae/bacteria), which can be toxic (cyanobacteria blooms) or harmful to the environment by creating low oxygen zones that are detrimental to fish and shellfish. Opening the cut improves the Pond’s health by allowing the pollution that accumulates in the pond to be flushed out and allows cool, clean, salty ocean water to wash in to the Pond through tidal flow. A successful opening will remain tidal for a week or two, during which healthy seawater circulates and mixes throughout the Pond. According to most experts, strategic pond openings are one of the best ways to improve pond ecosystems that are impaired by over nutrification, like Chilmark Pond.