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Boston Harbor and Massachusetts Bay
MWRA Environmental Quality Department

Boston Harbor


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. Long-term Harbor monitoring helps in identifying changes in water quality over time. Eight watersheds drain into the harbor; conditions in the wetlands, rivers, streams, groundwaters, and estuaries of Boston Harbor's watersheds are linked to the health of the harbor.

The Massachusetts Water Resources Authority monitors water quality at more than 50 locations in Boston Harbor.

Download Boston Harbor data below:

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.

Many reports on Boston Harbor and rivers are available on the Technical Reports List.


Questions or comments? Email us