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Boston Harbor and Massachusetts Bay
MWRA Environmental Quality Department

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Boston Harbor

Boston Harbor encompasses nearly 50 square miles and is an estuary, where fresh water from tributary rivers mixes with the salt water of Massachusetts Bay. The Boston Harbor watershed, or drainage basin, is the area of land that receives all the streams and rainfall to the harbor. There are eight main watershed areas that drain into Boston Harbor.

The Massachusetts Water Resources Authority monitors water quality at more than 70 locations in Boston Harbor and its tributary rivers. MWRA makes its sampling data available for download from the water quality data page.

Boston Harbor benefitted from the Boston Harbor Project, which improved sewage treatment and moved Deer Island Treatment Plant discharges from Boston Harbor to Massachusetts Bay.

More about Boston Harbor:

Boston Harbor beaches
Fish and Shellfish in Boston Harbor
Boston Harbor Project timeline

Available for download or printing:

How Clean Is Boston Harbor?
Bacteria in Boston Harbor
(PDF)
Reversing Eutrophication in the Harbor
Harbor beach fact sheets
State of Boston Harbor report series
Boston Harbor Water Quality Update (technical report, PDF)

Photo of sailboat in Boston Harbor
Sailboat in Boston Harbor

Boston Harbor Sampling Locations Harbor sampling locations