The Mystic River Watershed covers 76 square miles or roughly 1% of the land area of Massachusetts. It includes all the land area that drains into the Mystic River. Its headwaters begin in Reading, MA and form the Aberjona River, then flow into the Upper Mystic Lake in Winchester. From the Lower Mystic Lake, the Mystic River flows through Arlington, Somerville, Medford, Everett, Chelsea, Charlestown, and East Boston before emptying into Boston Harbor.
Water Quality Map
Each year the US Environmental Protection Agency issues a water quality grade for the Mystic River and its tributaries. Grades are based on data collected by our water quality monitors. Learn more about the 2018 water quality.