Charles River Dam
The Charles River Dam is a flood control structure on the Charles River in Boston Massachusetts, located just downstream of the Leonard P. Zakim Bunker Hill Memorial Bridge, near Lovejoy Wharf, on the former location of the Warren Bridge .

Also known as "The Gridley Dam", named after General Washington's first army engineer Col. Richard Gridley. Built and operational in 1978, the three locks can be crossed by pedestrians as well as bicyclists. It is part of the popular Boston Harborwalk. The dam contains three individual locks, with one wider than the other two to accommodate the occasional passing of a larger vessel. The structure also contains a fish ladder and a pump hydro-station, used when it becomes necessary to expel any accumulation of excess water from the river basin when the harbor tide level rises too high for a natural outflow to the harbor. Six diesel-powered, 2700 horsepower turbo-charged engines drive six pumps with a combined capacity of about 3.7 million gallons per minute. The purpose of the dam is to control the surface level of the river basin as well its tributary surfaces upstream, such as The Back Bay Fens and Muddy River and to prevent sea water from entering the Charles River freshwater basin during high tides. It replaced the Charles River Dam Bridge (older dam of 1912) upstream where the Boston Museum of Science is now located. The 1912 dam's one lock is now kept open for navigation. The older dam could not keep sea water out and a layer of salt water accumulated at the bottom of the fresh water basin, contributing to pollution and fish migration problems. The dam's walkway is the site of the "Charlestown Bells", an interactive art installation by Paul Matisse, consisting of a set of multicolored chimes mounted on the railing that passers-by can strike.