Editorial: Swimming in cities is a triumph of science and citizen action

In a pièce de résistance for swimmable cities, Paris’s Seine river is opening to swimmers for the first time in 100 years. Starting in late June, three free public access points will offer “Parisians and visitors a unique summer experience in and around the legendary river,” according to a website post by the French tourism office.

The French have pushed for swimming in the Seine since the 1980s. After the 2024 Paris Summer Olympics drew attention to the river’s pollution, the City of Light invested $1.5 billion in public works technology, including a massive underground stormwater overflow tank.

We applaud this milestone and the movement that campaigns for swimmable cities as a universal human right.

Many around the world agree. The Swimmable Cities alliance, founded in 2024, represents 72 cities and towns across 27 countries. By 2030, the nonprofit aims to sign 300 more cities to their charter and host three major summits in Rotterdam, the Netherlands; Copenhagen, Denmark, which likely has the cleanest urban river; and New York City. Politicians are getting on board, including London mayor Sadiq Khan, who, shortly after his 2024 reelection, pledged to make the Thames river swimmable by 2034.

As earth rapidly urbanizes, with more than half of the world now living in cities, green spaces are crucial.

As the alliance says on its website, “Swimmable urban waterways are vital to the livability of cities and communities, as shared civic places that promote the health of people (physically, mentally, spiritually) and the health of Mother Earth.”

While technological advances for reducing the pollution that enters waterways and legislation like the Clean Water Act in the US are both key, advances in clean water are often testaments to the dedication of individuals, whose everyday actions gradually build toward a better environment.

Since the first Earth Day in 1970, citizens worldwide have campaigned for plastic bag bans, planted trees, reintroduced native species, and participated in countless river cleanup days, methodically and slowly improving water health in places where easily enforceable laws have failed.

In the US, swimmable fresh water has been a goal of the Clean Water Act since 1983. The US is only halfway there, with 50 percent of assessed waterways still polluted, according to a 2022 report by the Environmental Integrity Project. Overflowing sewers contaminate water with human and animal waste containing viruses and bacteria such as salmonella and E. coli. Loopholes in the Clean Water Act continue to allow nonpoint pollution—usually nutrient-laden runoff from farms and city streets—to travel downstream. Nitrogen and phosphorus then spike the growth of algal blooms, which can be toxic to animals and wildlife.

But bright spots stand out—including the US capital, which is closer than ever to achieving the 1983 goal.

Nonprofits in Washington, DC, such as the Potomac Riverkeeper Network, already rely on the power of the public; 100 trained volunteers regularly sample water at more than 30 sites across the region as part of the group’s Community Science Water Quality Monitoring Program. This real-time research has revealed that at five testing sites from 2019 to 2023, it’s been safe to swim in the Potomac river on average about 70% of the time. What’s more, The DC-based nonprofit Potomac Conservancy, which scores the river’s health based on water quality data and other factors, most recently graded it a B, up from a D in 2011. And the Anacostia river, another DC waterway, scored its highest water quality grade in a decade in 2024.

In this next era of water conservation, swimmable cities will likely remain a symbolic milestone. After all, wading in a once-tainted river sends a resoundingly clear message to the public: “Come on in—the water’s fine.”

The editorial is the result of collective deliberation in C&EN. For this editorial, the lead contributor is Christine Dell'Amore.

Views expressed are not necessarily those of ACS.