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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

Recent Harbor Temperatures (NOAA)

Water Quality Parameter

Historic Range for Boston Harbor*


Dissolved Oxygen

1.35 -  14.31 mg/L   Mean: 7.75

Download physical data

(3566 readings)


49.5 -  79.6 deg F   Mean: 62.5
(3542 readings)


0.87 -  33.31 PSU   Mean: 29.91
(3395 readings)


6.85 -  8.66   Mean: 7.81
(3242 readings)

secchi disk2.jpg

Secchi Disk Depth

0.5 -  5.4 m   Mean: 2.22

Download clarity data

(1312 readings)
TSS 0.69 -  19.5 mg/L   Mean: 4.96
(706 readings)


Nutrient Chemistry

DIN: 0.22 -  11.25 umol/L   Mean: 3.44

Download nutrient data

(56 readings)

Chlorophyll & Phaeophytin

Chl a: 0.58 -  17.5 umol/L   Mean: 4.41
(699 readings)



0 -  73300 count/100 mL  Geo. mean: 2

Download bacteria data

(2162 readings)

E. coli

Parameter not tested

Fecal coliform

0 -  968000 count/100 mL  Geo. mean: 5
(2389 readings)

*For samples collected between June and October of each of the last five full calendar years, marine samples only.

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