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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


Get printable fact sheets on
the Harbor beaches.

Water Quality Parameter

Historic Range for Boston Harbor*


Dissolved Oxygen

1.29 -  14.31 mg/L   Mean: 7.6
(5221 readings)

Download physical data


46.2 -  74.9 deg F   Mean: 61.8
(5223 readings)


0.29 -  33.73 PSU   Mean: 29.68
(5015 readings)


6.47 - 8.66   Mean: 7.8
(4779 readings)

secchi disk2.jpg

Secchi Disk Depth

0.2 -  5.4 m   Mean: 2.21
(2027 measurements)

Download clarity data

0.69 -  20.2 mg/L   Mean: 4.59
(923 samples)


Nutrient Chemistry

DIN: 0.07 -  27.5 umol/L   Mean: 3.75 (229 samples)

Download nutrient data

Chlorophyll & Phaeophytin

Chl a: 0.53 -  17.5 umol/L   Mean: 3.94
(928 samples)



0 - 73300 count/100 mL  Geo. mean: 2
(3096 samples)

Download bacteria data

E. coli

Test not conducted in marine waters

Fecal coliform

0 - 968000 count/100 mL  Geo. mean: 7 (3485 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