MWRA submits reports to regulators on the quality of the treated wastewater, or effluent, being discharged to Massachusetts Bay from the Deer Island Treatment Plant. Our discharge permit also requires us to monitor the ecosystem of Massachusetts Bay, measuring the health of fish and shellfish, as well as nutrients, pathogens, metals, and toxicity. Any warning signs in the data are investigated to ensure they are not the result of the effluent outfall discharging into the bay. (See our pamphlet on Environmental Monitoring for more information.)
Massachusetts Bay Water Quality
- Contingency Plan threshold exceedance notice (6/10/25): Alexandrium catenella [PDF/834KB]
- Outfall Monitoring Overview [PDF/8.1MB]
- Bacteria Monitoring near the bay outfall
- Ambient monitoring quarterly
- Contingency Plan thresholds compared with ambient data [PDF/635KB]
- Water Column Monitoring Results [PDF/6.8MB]
Wastewater Treatment Measures
- Contingency Plan threshold exceedance: effluent acute toxicity (June 2025) [PDF/284KB]
- Discharge Monitoring Report for the Treatment Plant [PDF/124KB]
- CSO Discharge Monitoring Report for the CSO facilities [PDF/153KB]
- Contingency Plan thresholds compared with effluent monitoring data
- Infiltration and Inflow report [PDF/2.7MB]
- Demand Management, Flow Limitation [PDF/375KB]
- Deer Island Treatment Plant monthly performance [PDF/134KB]
- Treatment Plant annual maintenance
- Report Archive: See all Discharge Monitoring Reports
