Water Quality Monitoring Programs

Harbor and River Monitoring

The Massachusetts Water Resources Authority's (MWRA) has been monitoring water quality in Boston Harbor and its tributaries since 1989. The Harbor monitoring program is required by MWRA's National Pollutant Discharge Elimination System permit. All Harbor and tributary areas affected by combined sewer overflows (CSOs) in Boston, Chelsea, Cambridge, and Somerville are included in the monitoring program.

MWRA makes at least 20 visits to each sampling location every year. Some sampling locations in the Harbor are just visited between April and December because of freezing in winter. The locations are spread out, and measured in both wet and dry weather. Most of the waters included in this monitoring program are designated for recreational use (see table). Three bacterial indicators are and/or have been used to assess suitability for recreational use, fecal coliform, E. coli and Enterococcus.

Long-term Harbor monitoring helps in identifying change in water quality over time. Since MWRA was created in 1984, the Boston Harbor Project made significant improvements in the infrastructure of Greater Boston's wastewater treatment system. MWRA has also improved CSO treatment and control.

Massachusetts Bay Monitoring

The bay monitoring program measures water quality from stations near the outfall, to stations as far as Cape Cod Bay. "Nearfield" stations are located within seven kilometers (4.3 miles) of the outfall diffuser. "Farfield" stations include all stations in Boston Harbor; the coastal, offshore, and northern boundary regions; and Cape Cod Bay.

CSO Monitoring

The CSO monitoring area includes the "receiving waters" of all CSO communities in greater Boston. These areas include the Inner Harbor, Boston Harbor embayments, and tributary rivers. Monitoring focuses on measuring the water quality impacts of CSOs, i.e., bacteria and nutrient loadings. Dissolved oxygen, sewage indicator bacteria, nutrient concentrations and water clarity are also measured.

CSOs affect a large area of Boston Harbor, discharging along the shoreline into streams, rivers, estuarine areas and beaches. 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.

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. Monitoring of the beaches is carried out in conjunction with the Massachusetts Department of Conservation and Recreation. More information on these beaches is available on the Boston Harbor Beaches page.

Monitoring Results

Historical results from 1989 to 2004 for bacteria, nutrients, and other water quality parameters are available for download in Excel spreadsheets for the Harbor and three tributary rivers. There is also a monthly Harbor and River Water Quality Report that summarizes the most recent harbor data including Enterococcus, E. coli, chlorophyll, and water clarity.