There's something in the water - E.coli to be precise. After high levels of the bacteria were found in the Seine, questions were raised about how safe it would be for the triathletes and open water swimmers competing in the 2024 Olympics.
Meanwhile, just before the Oxford and Cambridge boat race in March, both teams were warned not to embrace the tradition of throwing the winning coxswain into the Thames: E.coli levels were 10 times higher than the reading given by the Environment Agency was considered 'poor'. .
Elsewhere in Europe, however, infections have largely declined in recent decades. In general it is is now safe to enter the water. In its latest report, published in June 2023, the European Environment Agency (EMA), which monitors more than 21,000 swimming spots across the continent (but no longer in Britain), found that only 1.5 percent had poor water quality.
Some lakes and rivers cross or line the continent's most alluring cities, making a dip a feasible part of a weekend getaway. The EEA has a handy mapping feature on its website that allows you to determine the location's water quality before you take the plunge.
Below, we highlight five places that are perfect for wild swimming - and four that you might want to avoid.
Where can you go wild swimming?
Vienna Austria
Austria came second after Cyprus in the latest EEA rankings for water quality, while Vienna authorities rated all of the city's seaside resorts as excellent during the 2023 season. At a popular spot in the city they even claim that the water rivals the "best lakes" in the country.
The Alte Donau, or Old Danube, was once a channel of the Danube River (until water management turned it into a lake in the 19th century), and is now so clear that you can see up to four meters below the water's surface. The vegetation is carefully managed and acts as a natural filter system, keeping twenty species of fish happy, while motorized vessels are prohibited.
In the summer months, outdoor swimming is as much a part of Vienna's routine as the daily commute, with locals visiting the Old Danube for swimming, sunbathing and sailing before eating at one of the restaurants along the coast. Others take the metro to Donauinsel (Danube Island) on the New Danube, with its volleyball courts, bars and 42km of beaches.
Zurich, Switzerland
Zurich borders a glittering lake and is bisected by a winding river. It's built on water - and the temptation to jump in is almost inevitable. During the summer, 30 outdoor swimming locations open and some locals even travel along the Limmat River to work, using the current to carry them to the city center.
However, this can be dangerous: visitors must stick to Zurich's designated swimming pools - or at the lake, where all EEA-monitored sites have been rated excellent.
Next to the affluent suburb of Seefeld, the towel-strewn lawns of Strandbad Tiefenbrunnen (entrance around £7) lead straight to the water and make a good spot for people-watching. Alternatively, for a more beachy feel, head to the sands of Strandbad Mythenquai, on the other side of the lake.
Bordeaux, France
Paris's water may be a little dirty, but another French city has changed its most popular seaside resort blue. In 2023, French authorities classified the water quality in Plage du Lac in Bordeaux as excellent.
A 10-minute tram ride north of the centre, this expanse of white sand on the edge of an artificial lake also regained its Blue Flag status in 2023. With a lifeguard on duty between June and September, it is ideal for families and there are toilets and showers on site.
About an hour's drive west, just before the balmy beaches at Arcachon, you'll find the pine-covered lakes of Carcans, and just south of Archachon Bay, Biscarrosse and Sanguinet, all rated 'Excellent' by the HONOR.
Berlin, Germany
It may have a reputation for clubs and cabaret, but Berlin also has one of Europe's healthiest wild swimming scenes, centered around the 3,000 lakes in the local region. Even in the swimming areas closest to the city, the water is rated as excellent by the EEA. Head to the non-touristy Strandbad Plötzensee (£7), where the hipsters hang out, Strandbad Weissensee with its sandy beach (£7) and Strandbad Orankesee (£6.85), with its child-friendly, spinning water slide in the water.
Meanwhile, about 25 minutes west of Berlin by S-Bahn, the sandy beach of Strandbad Wannsee stretches for more than 1,250 meters along the lake of the same name.
If you're willing to go a little further, it takes 45 minutes to reach Potsdam by S-Bahn, the former playground of the Prussian elite, home to 16 grand palaces spread across a wooded park. The lakes here, such as the Schlachtensee, are popular with Berliners in the summer.
Granada, Spain
Granada is far enough from the coast to make swimming in lakes and reservoirs popular, and the area has some brilliant places to dip your toes in the water - if you're prepared for a bit of adventure. About a 40 minute drive to the south west, the Los Bermejales Reservoir has an impeccable EEA record, and comes with Caribbean blue water, pine scented air and (unlike the Cubillas Reservoir closer to town, where currents can be very dangerous and it is best to stick to organized water sports), a shallow swimming area with a beach restaurant, attached to a campsite.
Although not rated by the EEA, the river pool at Restaurante Maitena on the outskirts of Güejar-Sierra is also a popular seaside resort, busy with rowers and divers in summer. The river pool in this hill town is a 30-minute bus ride from central Granada and is fed by runoff from the Sierra Nevada mountains.
And the cities to avoid
Brussels, Belgium
When sewers in this city overflow, waste goes straight into the canal, according to campaign organization Canal It Up, which also notes plastic and dead rats floating on the surface. No one would want to take a dip in this waterway - or the equally polluted River Zenne - which could explain why Brussels has not embraced open-air swimming: there is currently only one public outdoor swimming pool in the city.
Naples, Italy
The Sarno is regularly labeled as the most polluted river in Europe, because it collects both agricultural waste and inadequately treated wastewater. The river flows directly into the Mediterranean Sea at Rovigliano, just south of Naples. When campaign organization Goletta Verde analyzed the city's water in 2023, it discovered three particularly heavily polluted points, including the beach in the coastal district of San Giovanni a Teduccio.
Rotterdam, Netherlands
The Netherlands is one of only two countries rated by the EEA as 'poor' in three percent or more of its locations. The Netherlands has banned swimming in three recreational lakes in South Holland before 2024, including one in Rotterdam. It's due to pollution from toxic PFAs (chemicals used to make non-coatings, packaging, adhesives and electrical insulation).
Paris, France
Paris Mayor Anne Hidalgo has made it her mission to open three seaside resorts along the Seine to regular (non-Olympic) swimmers from 2025 and has even pledged to wade in herself before the Games, following suit a promise from Jacques Chirac. A clean-up operation aimed at improving wastewater disposal is underway, but whether her dream will become a reality remains to be seen.
