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, as described in the State of Boston Harbor Report.
Rain and snow on paved land leads to stormwater runoff that carries pollutants into the sewer system or nearby water bodies. Undeveloped land around Boston Harbor with natural vegetation acts as a filter to clean water that flows through its many layers of soil.
The Massachusetts Water Resources Authority
monitors water quality
more than 70 locations in Boston Harbor and its tributary rivers. Long-term Harbor monitoring helps to identify
changes in water quality over time.
MWRA makes its sampling data available for download from the water quality data page.