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Boston Harbor and Massachusetts Bay
Massachusetts Water Resources Authority


MWRA Water Quality Monitoring

Massachusetts Bay

MWRA's NPDES discharge permit for the Deer Island Wastewater Treatment Plant requires extensive monitoring and reporting.

MWRA monitors the effluent (treated sewage) that is discharged into Massachusetts Bay, to ensure that it meets the standards set out in the NPDES permit.

The Bay bacteria monitoring program, which measures water quality near the outfall to ensure that there is no risk to shellfish consumers.

The Ambient Monitoring Program addresses most Bay & outfall monitoring, as outlined in MWRA's Ambient Monitoring Plan.

Harbor & Rivers

The Massachusetts Water Resources Authority's (MWRA) has been monitoring water quality in Boston Harbor and its tributaries since 1989. MWRA makes at least 20 visits to each sampling location every year.

Monitoring areas are: Charles River, Mystic River/Alewife Brook, Inner Harbor, Northern Dorchester Bay/Carson Beach, Southern Dorchester Bay/Tenean Beach, Neponset River, and Quincy Bay/Wollaston Beach.


Water quality at Wollaston, Carson, Constitution, Tenean and Pleasure Bay beaches is tested by the Department of Conservation and Recreation (DCR) with assistance from MWRA.

Questions? Contact the Environmental Quality Department

Combined Sewer Overflows

The Combined Sewer Overflow (CSO) monitoring area includes the "receiving waters" of all CSO communities in greater Boston including the Inner Harbor, Boston Harbor embayments, and tributary rivers. Measurements include bacteria, nutrients, dissolved oxygen, and water clarity.

See map with sampling and CSO locations

CSOs discharge along the shoreline into streams, rivers, and estuarine areas. To allow for an intensive study of each affected body of water, receiving waters were divided into distinct geographic areas based on locations of tributaries and proximity to CSOs. Each area was monitored on a rotating schedule, with all areas sampled equally.

More information on CSOs

Monitoring Data

Long-term Harbor monitoring helps in identifying change in water quality over time. Historical results from 1989 to last year for bacteria, nutrients, and other water quality parameters are available for download in Excel spreadsheets for Boston Harbor and three tributary rivers.

Data Analysis & Interpretation

Summaries and technical analysis of MWRA water quality monitoring in Boston Harbor and Massachusetts Bay are available for download on our Technical Reports List.