Alewife Brook. (Photo by Isaiah Johnson)

NESTLED ON THE border of Cambridge and Arlington, the Alewife Brook Reservation is a serene urban wildland filled with wetlands, teeming with wildlife, and a popular oasis for residents. But it’s also the site where more than 1.6 million gallons of untreated sewage overflow — including human waste — have been dumped since the start of 2025. 

Despite tremendous progress made over the last 50 years to improve water quality throughout Greater Boston, outdated sewer infrastructure and underregulated stormwater practices continue to lead to the discharge of dangerous pollutants directly into our popular public waterways. A disproportionate number of the most egregious discharges, known as combined sewage overflows (CSOs), occur at Alewife Brook and along the Mystic River, a watershed region home to roughly 600,000 people. This poses a significant threat to their health and well-being, as well as that of critical ecosystems throughout the region.  

Fortunately, in 2025, we have an unprecedented opportunity to tackle this enduring challenge, which dates back to the cleanup of Boston Harbor, which began in the 1980s.

For the first time in a decade, we have a chance to take what we’ve learned about improving water quality and rewrite a roadmap that should include eliminating CSOs altogether, establishing foundational strategies to protect our waterways, and promoting climate-resilient infrastructure, public health, and ecological health. If we miss this chance, we risk missing a crucial window for making the water our residents and neighbors recreate in and live alongside safe for everyone to enjoy for decades to come. 

A kayaker paddling in the Mystic River basin. (Photo by Isaiah Johnson)

Constructed in the late 1800s, combined sewer overflows were designed as a connected sewer and storm drain system to ferry untreated wastewater and storm runoff into treatment plants. Today, these same pipes carry that mix of rainwater and sewage in the Boston area to the water treatment plant at Deer Island, during small rain events.  

When hit with moderate to severe rainfall events, however, these systems become overwhelmed, and — to prevent sewage from backing up into homes — divert untreated wastewater to outflows along our rivers and streams. These outflows expose communities to dangerous bacteria and other pollutants linked to severe health complications, and necessitate the all-too-frequent closure of local waterways, parks, and beaches.  

Unfortunately, incidents of discharges have become more common. As cities have grown and shifting rain patterns caused by climate change have brought heavier, more frequent precipitation events, our antiquated sewer system has struggled to keep up. Toxic water increasingly has no place to go but into areas where we work, play, and live.  

Indeed, even while dozens of CSO outflows in Boston, Cambridge, and Somerville have been eliminated over the past 35 years, over 100 million gallons of raw and partially treated combined sewage were discharged into the Mystic River and its tributaries in 2024 alone. In the recently published Mystic River water quality report card, one of these tributaries, the Alewife Brook, scored an alarming D+.  

This year, an update to the Massachusetts Water Resources Authority Combined Sewer Overflow Long Term Control Plan, which creates a 10-year framework for MWRA, local governments, and institutions to address the remaining combined sewer overflows impacting the Mystic, Neponset, and Charles rivers, as well as Alewife Brook, is well underway and set to be finalized and rolled out over the coming months.  

Combined with federal regulatory changes, the plan is in a position to substantially improve public health throughout Greater Boston and accelerate the progress made thus far in improving the water quality in the Mystic River watershed and the region. However, to be truly effective in ensuring our waterways are clean and safe from hazardous waste, the overriding priority of the plan must be to eliminate the discharge of sewage from combined sewer overflows completely.  

To accomplish this, any long-term control plan must be flexible and responsive to our rapidly changing climate, incorporating climate-ready solutions that prepare our cities for the heavy rain and snow events we can expect over the next decade. This means considering, whenever possible, green infrastructure solutions, such as rain gardens, bioswales, and stormwater wetlands, that provide co-benefits to communities most impacted by CSO discharges. 

Executing the long-term control plan must also be a collective effort involving municipalities, community groups, policy-makers, engineers, and the public. Transparency must be woven throughout the 10-year process — and this year’s negotiations — ensuring that infrastructure proposals are accessible to all and multiple opportunities are provided for the public to deliberate, share feedback, and react to proposals.  

Together, these essential investments in infrastructure and planning present a massive opportunity to modernize our infrastructure and better protect our waterways to reflect and serve everyone in our communities. We can no longer afford to kick these urgently needed updates down the road.  

In the 1980s, Massachusetts embarked on a massive operation to clean up Boston Harbor. Today, we are reaping the benefits of that effort — proving that we can innovate to tackle big infrastructure challenges with massive and long-term payoffs for the public good.  

We now find ourselves at another pivotal moment in the quest to improve water quality. It’s time to step up, eliminate CSOs, and implement a sustainable, long-term plan to protect the Mystic River and Alewife Brook, so that residents living along these waterways will have access to clean, healthy water now and into the future. 

Andy Hrycyna is the water quality program manager and Marja Copeland is the stormwater projects manager at Mystic River Watershed Association.