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Updated CSO Control Plan

INTRO

Combined sewer overflows (CSOs) happen when heavy rain overwhelms sewer systems that carry both stormwater and sewage, causing a mix of runoff and wastewater to be released into public waterways (including the Charles River).

Recommended reading: Massachusetts Rivers Alliance’s clear, informative explainer on CSOs.

To comply with the EPA’s Clean Water Act, the MWRA, Cambridge, and Somerville must draft, present, and execute a CSO Control Plan within a legally enforced framework, structured timeline, and public engagement.

View project information, timeline, and meeting materials on the CSO Control Plans website.

OUR ADVOCACY PRIORITIES

We believe everyone deserves a core memory on the Charles, and we believe this is a once-in-a-lifetime opportunity for Massachusetts to invest in clean rivers for the public health benefit, quality of life, and climate resilience of future generations.

The CRC is committed to a constructive, collaborative approach in working with stakeholders. We stand alongside partners like the Charles River Watershed Association, Mystic River Watershed Association, and Save the Alewife Brook in calling for the strongest level of CSO control. Raw sewage does not belong in our rivers.

Our role is to help bridge the gap—to work with agencies, municipalities, and residents to identify solutions that are both ambitious and achievable, and to build the public support necessary to implement them.

PUBLIC COMMENT PERIOD IS OPEN

The City of Cambridge, the City of Somerville, and the Massachusetts Water Resources Authority (MWRA) have submitted the Draft Updated Combined Sewer Overflow Control Plan (Draft Plan).

View Draft CSO Control Plan Documents

Public comments on the Draft Plan can be submitted to the project team through an online comment portal, by email (UpdatedCSOControlPlan@aecom.com), or by mail through September 30, 2026.

Written comments addressed to “Draft Updated CSO Control Plan Partners” can be mailed to the project team at the following address: 

MWRA 
Attn: Draft Updated CSO Control Plan 
2 Griffin Way 
Chelsea, MA 02150 

TIMELINE FOR NEXT STEPS

  • Draft Updated CSO Control Plan submittal will be followed by public meetings and hearings within a five-month MassDEP/EPA and public review period through September 30, 2026.
  • The Variances require that a Final Updated CSO Control Plan, which addresses comments received on the Draft Updated CSO Control Plan, be submitted for review by the Massachusetts Environmental Policy Act (MEPA) office by January 31, 2027.
  • The Variances also provide that during the period between January 31, 2027 and August 31, 2029, MassDEP, in coordination with EPA, will review the Final Updated CSO Control Plan, review and consider public comments on the Plan, confer with the MEPA office, and take action to approve or disapprove the Plan.

HOW DID WE GET HERE?

On February 25, 2026, the MWRA Board of Directors voted “YES” to approve staff’s recommendation of the “2050 Typical Year” plan, which will allow raw sewage to be dumped into our waterways for generations. We are disappointed that the MWRA did not vote for the strongest level of control (“Zero CSO discharges in a 2050 25-year, 24-hour design storm”) to eliminate sewage overflows in the face of worsening climate change—especially when the difference in cost to MWRA ratepayers between the approved plan and the plan preferred by advocates is less than $4 per household per month.

CRWA Press Release
MyRWA Press Release

Although we are encouraged that the MWRA Staff has chosen a stronger level of control than previously presented (and has since abandoned its proposal for “Future Change in Water Quality Standards”), we ask the MWRA to choose the most ambitious plan that creates and sustains a healthy, resilient Charles River, Mystic River, and Alewife Brook.

GET INVOLVED

Take action: In addition to leaving public comment on the CSO Draft plan, write to Governor Healey, EEA Secretary Rebecca Tepper, and your elected officials (find your legislators) to share your disappointment with MWRA’s Draft CSO Control Plan, why you believe sewage does not belong in our rivers, and ask them to invest in the long-term benefits the strongest level of CSO control delivers for the people of Massachusetts. We encourage you to share your personal experience with the river and why a clean, swimmable, healthy Charles River matters to you!

LATEST PRESS

2026

2025

UPDATES

May 18, 2026: The project team will host a Virtual Public Meeting on June 2, 2026 to describe the contents and details of the Draft Plan. This meeting is informational only; public comment will not be solicited during this meeting. Oral public comments will be solicited and entered into the public record at two public hearings in September. Written comments will be accepted throughout the entire comment period (May 1 – September 30, 2026).

Register for Virtual Public Meeting

Mar. 3, 2026: The Charles River Conservancy has submitted a letter to Governor Healey re: the CSO Long-Term Control Plan approved by the MWRA Board.

“We urge you to call on the MWRA to “be the hero” to design and implement a world-class, climate-resilient system that virtually eliminates sewage discharges to the Charles River, Mystic River, and Alewife Brook, and that ratepayers can take pride in funding as a legacy.”

Feb. 5, 2026: MWRA Feb 4 board meeting materials are available for review. In short, the four levels of CSO Control currently under evaluation by MWRA Staff:

  • significantly reducing CSO discharges from those predicted to occur in a 2050 Typical Year (“Limited CSOs in the 2050 Typical Year”) → MWRA’s recommendation on October 29, 2025
  • Zero CSO discharges in a 2050 Typical Year (“2050 Typical Year”) → MWRA’s updated recommendation on Feb 4, 2026
  • Zero CSO discharges in a 2050 5-year, 24-hour design storm (“2050 5-year”)
  • Zero CSO discharges in a 2050 25-year, 24-hour design storm (“2050 25-year”) → strongest level of control, the preference of Massachusetts rate payers and environmental advocates

Staff will request approval from the MWRA board to move forward with the draft plan in the MRWA board meeting (hybrid) on Wed Feb. 25 at 1pm.

Jan. 21, 2026: MyRWA issued a comprehensive (and illuminating) recap of the most recent CSO Public Meeting. We highly recommend reading this clear, easy-to-digest summary.

Jan. 15, 2026: Explore presentation materials, public comments, and meeting recording from the public meeting #6 (held Jan. 15, 2026) presented by the joint CSO Control Plan team (MWRA and the Cities of Cambridge and Somerville) re: “Updated Results of Alternatives Screening.”

Jan. 15, 2026: MWRA Executive Director Fred Laskey has announced his retirement after 25 years with the authority. Thank you for your service and leadership overseeing the Boston Harbor’s cleanup and transformation.

Nov. 19, 2025: A motion in court to intervene in the ongoing federal lawsuit that led to the cleanup of Boston Harbor has been filed by the Charles River Watershed Association and Mystic River Watershed Association.

“Given deep concerns that MWRA’s recent proposal signals that the Authority has no intention of making further meaningful efforts to reduce and eliminate CSOs, CRWA and MyRWA have asked the court to be added as parties to the case in order to have a say in how the issues get resolved.”

Nov. 13, 2025: As a follow-up from their previous announcements they would be addressing their CSO Control Plan and change in water quality standards at the Nov. 19 Board Meeting, MRWA has decided to remove this topic (and vote) from the agenda for the time being. We are encouraged by MWRA’s reception and consideration of significant public feedback. For community advocates who support a NO vote, our attendance at the Nov. 19 meeting is no longer necessary. However, the work is not yet over.

Oct. 31, 2025: CRC Executive Director Laura Jasinski puts out a call to action to protect our river’s water quality standards, uphold the vision held by the EPA Clean Water Act and the Charles River Initiative for a fishable and swimmable river, and invest strategically in the Charles River’s resilience.

Oct. 29, 2025: MWRA Board of Directors meeting materials includes verbiage that considers a support for “future change in water quality standards” in order to fulfill legal compliance to the EPA’s Clean Water Act and Clean Charles River Initiative.