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The cleanup of Boston Harbor is incomplete

Largely unknown to the public, raw sewage is still dumped into the Mystic and Charles rivers, which empty directly into the harbor.

Scientist Scott Smith and actor Mark Ruffalo work in the Charles River in 2014. The actor, in town to film the movie "Spotlight," helped with water testing near an outfall pipe into the river.Suzanne Kreiter/Globe staff

The cleanup of Boston Harbor is considered one of the great environmental success stories of our time — and deservedly so. It has helped transform the quality of life in the metro Boston area as residents and businesses live, work, and play near the newly cleaned up harbor and the rivers that feed into it.

But sadly, and largely unknown to the public, raw sewage is still dumped into the Mystic and Charles rivers that empty right into the harbor. Depending on the volume of rainfall and snowmelt, up to 500 million gallons of sewage mixed with storm water are discharged into the harbor via the two rivers every year.


These discharges flow from old underground pipe networks known as combined sewer systems, engineering relics that were designed to collect rainwater runoff, domestic sewage, and industrial wastewater in the same pipe leading to a treatment plant. But during periods of heavy rainfall or snowmelt, the wastewater volume can exceed the pipe’s capacity, causing a combined sewer overflow, or CSO, that dumps the polluted contents directly into the rivers.

This year marks the 50th anniversary of the Clean Water Act. Relying on sewage infrastructure that was designed in the 1800s is the equivalent of continuing to travel by horse and buggy. Massachusetts must do better, and needs to do it now as climate change brings more intense storms, more severe flooding, and more sewage overflows.

The landmark litigation that began in the 1980s and catalyzed the Boston Harbor cleanup charged the newly created Massachusetts Water Resources Authority with developing and implementing a long-term control plan for reducing CSO discharges. To its credit, the MWRA has made dramatic progress.

Prior to the cleanup, a staggering 1.7 billion gallons of polluted wastewater were discharged annually into the lower Charles between the Watertown Dam and Boston Harbor. That volume has been reduced to no more than 500 million gallons from CSOs in the past few years.


Yet despite considerable investment, the MWRA is poised to fall short of targets set in its plan, which still allows for 85 million gallons of combined sewage discharge into the Charles and Mystic river systems annually. Currently, 16 CSO outfalls remain that did not achieve the levels mandated by the court within the 20-year time frame. Six of these outfalls are expected to achieve compliance by 2024, and the MWRA has developed conceptual plans which, if implemented, may help address an additional four. But there is no plan for bringing the remaining six outfalls — five in the Charles and one in the Mystic — into compliance.

Indeed, the MWRA in 2021 requested a three-year extension for compliance to 2024 and expressed concern about whether the costs to achieve compliance would be worth the benefit.

Boston Harbor was once considered the most polluted harbor in America, and cost was the argument raised by generations of political leaders as the reason not to clean it up. If we had listened to those voices, we would not have spent the $4.5 billion to clean the harbor and enable a thriving waterfront and enviable urban beaches that have together become an economic driver of the entire region.

Granted, there is fierce competition for public dollars. But there have been many technological advances in CSO control since the 1990s, when infrastructure planning began. Experiences in other cities have shown that installing green infrastructure in CSO drainage areas is particularly cost-effective — think of rain gardens, porous pavement, and green roofs — for temporarily storing the rainwater and keeping it from overwhelming the system.


An incomplete cleanup of Boston Harbor, with potentially hundreds of millions of gallons of sewage flowing into the Charles and Mystic rivers and ultimately into Boston Harbor every year, as climate change only fuels the problem, is unacceptable.

Massachusetts residents should not settle for less than healthy rivers and harbors. Federal infrastructure funds are available for exactly the kinds of efforts needed to reduce and finally eliminate CSOs.

Only then will the task of cleaning up Boston Harbor be truly worthy of the praise heaped upon it.

Patrick Herron is executive director of the Mystic River Watershed Association. Emily Norton is executive director of the Charles River Watershed Association.