Mill Pond Herring Run protection


Mill Pond in historic Marstons Mills dates to the 17th century when part of the Marstons Mill River was dammed to power a gristmill on its shores.

Today, Mill Pond is one of the most photographed bodies of water on Cape Cod. It’s beautiful, with serene white swans gliding on its crisp, blue surface, an image easily lifted from a 19th century postcard. Mill Pond, tucked into the intersection of Routes 28 and 149, is a scenic wildlife refuge and active herring run for fish making their way upstream to spawn in Middle Pond.

The real story about Mill Pond, however, is far different from a bucolic postcard or vacay smartphone pic. Just below its surface, Mill Pond is filthy and its waters are impaired. Over time, the man-made construction of the dam has trapped and contained thick, black sediments in a geologic kitchen sink that is filled to overflowing with nitrogen and phosphorus. These contaminants make their way downstream into the Three Bays estuary, heavily contributing to excess nitrogen in the very estuarine system we should be protecting.

In fact, with the help of a dedicated corps of volunteers, Barnstable Clean Water Coalition conducts an annual herring count near a culvert on the south end of Mill Pond. In recent years, we’ve recorded fewer and fewer fish that use this historic waterway to reach spawning grounds. To environmentalists and ecologists, herring are like canaries in a coal mine; their presence or lack thereof could keenly indicate trouble within the watershed.

Barnstable Clean Water Coalition has studied the Mill Pond crisis for years. We’ve come up with a science-based solution to restore this impaired and historic waterway.

The Mill Pond restoration plan includes dredging and beneficial re-use of the accumulated deposits in landscaping projects. The project has a limited sediment dredging area that preserves shallow water habitat for the endangered Bridle Shiner that resides there. Dredging is intended to improve the movement of water through the pond, elevate water quality measurements, and bolster overall ecology of Mill Pond to benefit downstream systems. The dredging materials will be de-watered on a town-owned lot north of the pond, and accumulated deposits can then be used as a soil conditioner in landscaping projects.

The pathway toward restoring Mill Pond also includes a pilot project for floating wetlands. These man-made “floating islands” treat the pond water. Plants’ root zones provide valuable habitat for fish and microorganisms while reducing nitrogen and phosphorus levels. Our well-researched plan identifies an area in the northern reach of the pond where a ring of floating wetlands could provide a treatment barrier to intercept and process incoming waters from the Marstons Mills River. These wetlands could be anchored to the bottom of the pond or could be supported by a floating dock system to access wetland systems for maintenance and monitoring.

Barnstable Clean Water Coalition is currently monitoring the nitrogen/phosphorus levels and water flow throughout the Mill Pond system (inlet and outlets) to determine precise levels of nitrogen/phosphorus that are potentially flowing into our bays.