Sesachacha And Hummock Ponds Opened To Ocean

Two of the island's Great Ponds were opened to the Atlantic Ocean this week by the town of Nantucket's Natural Resources Departments.

An excavator dug a cut between Sesachacha Pond and Nantucket's eastern shoreline on Wednesday, and Hummock Pond was opened the following day on the other end of the island. The openings are done twice per year at each of those ponds as a hydraulic management technique to facilitate the dilution of high-nutrient pond water with low-nutrient ocean waters, according to the town.

"In general, openings last one to three weeks, lower the pond by about half its volume, and refill it to about the 75 percent mark," the town stated in an announcement this week. "The remaining 25 percent of pond volume is refilled more gradually by groundwater and direct precipitation, with refill requiring at least a month, longer during dry periods. There is variation in the duration of opening and change in pond volume, and the impact varies along a gradient from ocean to inland...In addition to flushing of the pond, openings also allow access for anadromous fish (fish that spend most of their lives in saltwater and return to freshwater to spawn)."