The Cleanup of the Charles River: An Urban Pollution Success Story

By Lauren von Aspen

The 80-mile Charles River, running from Hopkinton to the Boston Harbor, is an iconic Massachusetts feature and the most prominent urban river in New England. The river was once used for a variety of recreation activities including swimming and fishing, but in the mid-20th century, the water was deemed unsafe for recreation due to over urban pollution. But in 1995, an initiative by the Environmental Protection Agency in conjunction with state and local agencies, nonprofits, and citizens, sought to make the river safe again. Since then, the Clean Charles River Initiative has made significant progress in reducing bacterial and sewage pollution. 

The pollution of the Charles River is due in part to the design of Boston’s sewer systems. The pipes are designed to carry sewage and stormwater together to a treatment facility, where both types of wastewater are cleaned and released. However, during times of potential overflow (such as heavy rain or snowmelt) the pipes safety valves are triggered, which releases the sewage/stormwater directly into the river. This is referred to as a combined sewer overflow (CSO). One of the most notable successes of the initiative has been that, through work with treatment facilities, the Massachusetts Water Resource Authority has successfully cut CSOs by a remarkable 99.5% since their 200 settlement with the EPA. The overall amount of sewage-contaminated water flow into the river has also significantly decreased, with one million gallons a day eliminated from the municipal systems stretching from Watertown to the Boston Harbor, and 48,000 gallons a day eliminated from lower Charles municipalities including Boston, Cambridge, Newton, Brookline, Watertown, and Waltham. 

So, is the river safe to swim in? 

The EPA evaluates the health of the river yearly based on factors such as E. coli and blue-green algae presence. As of 2023, the lower basin (where Boston is located) was evaluated at a B-, meaning the river is actually safe for swimming and boating most of the time, and the EPA states that it is safe 70% of the time. This is a step up from its D grade in 1995, when it was almost never safe for swimming. However, residents are still not allowed to swim in the river except for on specially-permitted occasions. This is less attributed to problems with pollution and more due to the lack of safe swimming infrastructure in the river. But there is one time a year, during the City Splash event, that Bostonians can cool off from the summer heat with a dip in the Charles. It’s an event organized by the Charles River Conservancy, an organization that seeks to “make the Charles River and its parks a well-maintained network of natural urban places”. Their Swimming Initiative has organized City Splash since 2013 in a demarcated deep-water section of the Charles River with a Special Use Permit from the state. 

Despite now being one of the cleaner urban rivers in the United States, many living there are still skeptical. One Boston resident, Marc Gildenhuys, states that few people he’s known have ever swam in the river, and those who have “are considered in certain circles to be brave.” He cited concerns over pollution and bacteria, in addition to the cold. While there is still a ways to go before the Charles River can reach its full recreational and ecological potential, the EPA initiative has been largely successful in cleaning up the infamous “Dirty water” of the river.

Citations

“Charles River | River, Massachusetts, United States.” Encyclopedia Britannica, 25 Jan. 2025, www.britannica.com/place/Charles-River.

“Charles River Swimming Initiative.” Charles River Conservancy, Charles River Conservancy, 2023, thecharles.org/our-work/charles-river-swimming-initiative/. Accessed 16 Mar. 2025.

“Environmental Challenges for the Charles River.” US EPA, United States Environmental Protection Agency, 22 Aug. 2014, www.epa.gov/charlesriver/environmental-challenges-charles-river.

“The Charles River Initiative.” US EPA, United States Environmental Protection Agency, 22 Aug. 2014, www.epa.gov/charlesriver/charles-river-initiative.

Wikipedia Contributors. “Dirty Water.” Wikipedia, Wikimedia Foundation, 23 Sept. 2019, en.wikipedia.org/wiki/Dirty_Water.