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Boston Harbor and Massachusetts Bay
Massachusetts Water Resources Authority

Boston Harbor & Tributary Rivers

Boston Harbor Page Harbor Beaches Page Charles River Page Mystic River Page Neponset River Page
Boston Harbor Beaches Charles River Mystic River Neponset River


Boston Harbor encompasses nearly 50 square miles and is an estuary, where fresh water from tributary rivers mix with the salt water of Massachusetts Bay. Learn more about Boston Harbor.

The Massachusetts Water Resources Authority monitors water quality at more than 50 locations in Boston Harbor. Measurements are also made in the Charles, Mystic, and Neponset rivers. The monitoring program is designed to monitor the impacts of combined sewer overflows (CSOs) on the Harbor and rivers.

Click on this Boston Harbor sampling map for additional stations and station numbers
See larger map with sampling locations


Water Quality Parameter

Historic Range for Boston Harbor*


Dissolved Oxygen

1.29 -  14.31 mg/L   Mean: 7.54
(7886 readings)

Download physical data


46.2 -  74.9 deg F   Mean: 60.9
(7978 readings)


0.29 -  33.73 PSU   Mean: 29.75
(7800 readings)


6.47 -  9.95   Mean: 7.82
(6922 readings)

secchi disk2.jpg

Secchi Disk Depth

0.2 -  6.9 m   Mean: 2.39
(3300 measurements)

Download clarity data

0.37 -  20.2 mg/L   Mean: 3.85
(1981 samples)


Nutrient Chemistry

DIN: 0.03 -  27.5 umol/L   Mean: 3.15(783 samples)

Download nutrient data

Chlorophyll & Phaeophytin

Chl a: 0.53 -  18.4 umol/L   Mean: 3.75
(1994 samples)



0 -  169000 count/100 mL  Geo. mean: 2
(4531 samples)

Download bacteria data

E. coli

0 -  261000 count/100 mL  Geo. mean: 3(2372 samples)

Fecal coliform

0 -  968000 count/100 mL  Geo. mean: 7(2706 samples)

Some Boston Harbor/River Reports found on the Technical Reports List

An update of water-quality improvements in Boston Harbor

Patterns of wastewater, river and non-point source loadings to Boston Harbor

Trends in sediment contaminant concentrations in northern Dorchester Bay

Boston Harbor: a comparison of eutrophication-related water quality

Summary of CSO receiving water quality monitoring in Upper Mystic River/Alewife Brook

Update of patterns of wastewater, river and non-point source loadings to Boston Harbor

Receiver operating characteristic (ROC) curve analysis of antecedent rainfall

Eutrophication of the lower Charles, Mystic and Neponset rivers, and of Boston Harbor

Questions or comments? Email us