In 2019, several years before Olympic athletes dove into the Seine, a group of friends sought a place to swim in Metz, three hours east of Paris. Summers were getting hotter, and most municipal pools were either closed or at capacity. The group wanted to create a swimming area in the Moselle River, which originates 125 miles from Metz in the Vosges Mountains, and flows through the French city of roughly 117,000 people.
“It’s swimmable most of the time,” said Sibylle van der Walt, who spearheaded the group. “It’s much better than the Seine.”
They established Metz Ville d’Eau, a grassroots environmental organization, and partnered with university researchers to begin testing water quality at different sites along the river. So far, bacteria levels have generally been safe except after heavy rain, including in the Canal de Jouy area, which had a river pool from 1934 until 1982. Full results are expected in May 2025, according to van der Walt.
Metz Ville d’Eau is part of the swimmable cities alliance, representing organizations from 31 cities in 16 countries that are pushing for cleaner and more accessible urban waterways. Last month, the alliance published a charter that lays out its principles and goals—including establishing 30 swimmable cities by 2030.
The group wants “a new status quo” of public access to urban waterways for swimming. Depending on the city and the waterway, that could be as simple as allowing swimming in a formerly polluted river where conditions have improved. Or it could require rewriting laws to allow filtered floating pools in rivers or periodically close waterways to shipping, for instance.
By creating a global umbrella for urban swimming initiatives, the organizers say, they hope to foster an exchange of ideas and prototypes. What works in New York or Paris or Metz could help guide efforts in other places.
“Instead of people trying to create the same solutions independently, can we work with those that have already been developed?” said Matt Sykes, founder of Regeneration Projects, a Melbourne-based sustainability consultancy that started the alliance.
How the Seine River went from toxic dump to ‘economic engine’
Plans for an inaugural summit in Paris next summer have support from the city’s deputy mayor. van der Walt hopes that the summits encourage funding from cities or the European Union, helping more river pools and beaches to launch. But the Seine’s transformation for the Paris Olympics may ultimately be what ushers swimmable cities into public consciousness and moves projects forward.
Paris invested $1.5 billion in a stormwater storage tank, equivalent to 20 Olympic-size pools, to hold toxic runoff that would otherwise end up in the Seine. Three public swimming areas are scheduled to open next summer, including near the Eiffel Tower, where ships will be banned between 10 a.m. and 6 p.m.
“The public authorities will not be able to say, ‘Oh, it’s too complicated. We can’t do this.’ If it’s been done in Paris, you can also do it in Toulouse,” van der Walt said, citing another French city striving for a swimmable river.
Until this summer, swimming had been banned in the Seine since 1923. Like many urban rivers, it had been a catchall for raw sewage and toxic runoff (globally, more than 80% of untreated wastewater flows back into the environment). Tourist boats and commercial shipping vessels have dominated the river, a thoroughfare for about 20 million tons of freight each year.
That’s all changing, but not without a few hiccups. The Olympic men’s triathlon was postponed due to bacteria from sewage overflow. Later, a Belgian triathlete reportedly fell ill after swimming in the river, leading her team to drop out of the event.
While the Olympics may help “capture the public’s attention about swimmable waterways,” the triathlon snafu also underscores that “for too long, we’ve treated our rivers like open sewers,” said Marc Yaggi, CEO of Waterkeeper Alliance, a clean water advocacy organization and member of the swimmable cities alliance.
The benefits of urban swimming
Reversing those practices can go beyond restoring biodiversity (the Seine has more than 30 fish species now, up from three in the 1970s). Cleaner waterways are pivotal to more equitable cities, creating public spaces that support health, economic growth, and climate resilience. Swimming can be “an economic engine,” said Yaggi. “A swimmable city can drive tourism and recreation and local business developments. You’ve got a platform for environmental education, and a climate solution in terms of giving people a place to cool off during heat waves.”
Swimming contributed roughly $3 billion in social value to England in 2022, according to Swim England, a non-profit organization that promotes and develops swimming in England, with benefits ranging from improved physical and mental health to reduced crime. London-based architect Chris Romer-Lee hopes to expand those benefits by creating swimming areas on the River Thames. His firm, Studio Octopi, a member of the swimmable cities alliance, initially proposed the Thames Baths in 2013.
Multiple sites along the the Central London section of the river have been considered, but “the old rules that dictate how the river is run” have thwarted each attempt, Romer-Lee said. The Port of London Authority (PLA) discourages swimming in the Thames. And on top of construction costs, the pools would owe rent to the PLA for using moorings, which are in short supply on the river. Those fees would put a public pool out of business “within a couple of years,” Romer-Lee said. “There needs to be a bit of flexibility in how the authorities deal with a not-for-profit community enterprise such as Thames Baths.”
That seems more likely than even a year ago, given London Mayor Sadiq Khan’s recent proposal for a swimmable Thames by 2034. Moreover, +Pool helped achieve policy changes to encourage filtered floating pools in New York, offering a potential template for other large cities. Additionally, London recently completed its $6 billion Tideway Tunnel, a container to prevent 600 Olympic-size pools worth of sewage overflow from entering the Thames. It won’t capture all of the pollution from tributaries that feed the river, but a “sponge city” approach using permeable surfaces and green spaces “for water to collect before it goes into the river” could help, Romer-Lee said.
Citizens filling in the gaps
In cities lacking funding or political will, people often swim anyway, risking their health by trespassing in polluted rivers. Many places rely on grassroots efforts to mitigate, or at least raise awareness of, some of the risks. Open swims on the Milwaukee River have highlighted poor water quality there. Lake Ontario Waterkeeper created Swim Guide, an app using citizen science and government data to determine swimmability in over 10,000 locations. Efforts by London Waterkeeper resulted in a map of real-time sewage overflow data in 2023.
Despite so much information, there’s “not nearly enough,” Yaggi said. “We know exactly how much carbon and methane is being emitted into the atmosphere, but we don’t know what’s in our water, even though we have tons of data on it.”
The cost of comprehensive water quality monitoring exceeds what some local and state governments—and the U.S. federal government—are willing to invest, according to Yaggi. Moreover, most water quality monitoring focuses on bacteriology—E. coli and Enterococcus—but van der Walt points out that chemical concentrations in the water and the riverbed can get overlooked.
This summer, thanks to advocacy by Metz Ville d’Eau, the mayor of Metz created a small sandy beach on the Moselle. But the riverbed is polluted with arsenic, according to chemical testing by Metz Ville d’Eau partners, potentially putting swimmers at risk when they use the new shallow swimming area. In addition to the small beach, Van der Walt and her friends are still seeking the city’s approval for a filtered river pool in a deeper area of the Moselle. There will be opportunities to lean on the alliance for support, including a planned 2027 summit in Copenhagen to mark the 25th year of Islands Brygge, a harbor bath considered a model for urban swimming. The publicity surrounding the cleaning up of the Seine “might help us further,” she said.
“It’s a new phase in the French context,” van der Walt added. Just as cities built for cars are recognizing the need for pedestrian and cycling lanes, she said, municipalities that have prioritized industrial uses of rivers “are suddenly confronted with the fact that there could be other users of water.”