The Mystic River is the name of a short river in the Commonwealth of Massachusetts in the United States. Its name derives from the Native American word "Missi-Tuk", which translates to "great tidal river", and it lies to the north of and flows approximately parallel to the Charles River. Mystic River has a long history of industrial use and a continuing water quality problem. Encompassing 76 square miles (197 km²) of watershed, the river flows from the Lower Mystic Lake, and travels through the Boston, Massachusetts area communities of Arlington, Medford, Somerville, Everett, Charlestown, Chelsea, and East Boston. The river joins the Charles River to form inner Boston Harbor. Its watershed contains 44 lakes and ponds, the largest of which is Spot Pond in the Middlesex Fells, with an area of 307 acres. Extensive salt marsh lined the banks of the Mystic until 1909, when the first dam was built across the river (Craddock Locks), converting salt marsh to freshwater marsh and enabling development. Today's dam, named for Amelia Earhart, was built in 1966. It has three locks to allow the passage of boats, and is equipped with pumps to push fresh water out to the harbor even during high tide. Dam operators leave the locks open at times to allow the passage of fish. There is a fish ladder, but it has never been functional. The dam is closed to the public. At one time, the Mystic River was home to great numbers of many species of fish, including salmon, alewife, blueback herring, striped bass, bluefish, smallmouth bass, largemouth bass, bluegill, carp, and more. Although most of these species still live in the Mystic River, pollution and dam building have severely damaged the populations. Pollution came from various mills and a small ship building yard in the past. The main source of pollution in the 20th century and into the present is from drainage from the adjoining cities. Many of the records of nearby drainage pipes have been lost, or have undocumented changes and diversions. Once described as having so many herring that one could cross the river on their backs, the Mystic River herring run is much smaller than it was in historic times. This can be attributed to the pollution and dams.
Be warned.... No one should consume any fish from this water body. It contains deadly levels of the contaminants PCBs, Chlordane and DDT! http://www.mass.gov/Eeohhs2/docs/dph/environmental/exposure/fish_consumption_advisory_list.pdf