Olympic triathletes had to contend with the same risk this summer in Paris, where they competed in the Seine after a €1.4bn effort to make the river swimmable for the first time in over a century. Poor water quality still forced organisers to postpone the big day and several athletes reportedly fell sick after their races.

The incident put a prime-time glare on an emerging political issue in Europe. Many cities like Ghent have medieval roots and centuries-old infrastructure that haven’t been updated to handle the huge uptick in waste that’s discharged from homes and factories. In the UK, sewage spills into rivers and the sea have caused widespread public outrage. Meanwhile, climate change is bringing wetter weather that can cause flash floods and overwhelm sewer systems.

The European Union this year updated three-decade-old rules for how countries must collect and treat their wastewater, but many are still failing to comply with older laws. The European Commission is currently taking legal action against Italy, Greece and Spain for not reaching clean water standards that should have been met years ago.

European nations also face a separate 2027 deadline to improve the health of their rivers, lakes and seas. The most recent update, in 2021, found that two-thirds of the continent’s surface water hasn’t improved enough.

“It's a lurking problem for many river cities and communities around the world,” says Mina Guli, a businesswoman who undertook a long-distance run along the Seine before the Olympics to raise awareness about river pollution. “What we are seeing now with the Seine and what we're seeing in the UK is a little bit of a canary in the coal mine.”

Sewage needs to be treated in several stages before it can be safely returned to the environment. The first filters out solids, the second removes harmful chemicals and reduces nutrients such as phosphorus and nitrogen which lead to harmful algae growth, and the steps after that disinfect the wastewater and remove more nutrients.

Sewer systems

Some 20% of people in the EU live in places where only the first step occurs. An unknown amount of sewage is never treated at all — or only screened very cursorily — because it overflows from the sewers before it ever reaches a treatment plant.

That’s because European countries are very reliant on sewer systems known as Combined Sewer Overflows (Csos), which act as a relief valve during heavy rain. The pipes channel excess rainwater, micxed with sewage, into open water bodies to prevent flooding or even water backing up into homes. Most of these systems were built in the 19th and 20th centuries. Regions with newer sewer systems, like Australia and the western US, tend to collect rainwater and sewage separately, especially outside of cities.

“It was cheaper to build a single pipe than build completely separate pipe systems,” says Alastair Chisholm, director of policy at the UK’s Chartered Institution of Water and Environmental Management, an industry group. “If you were putting them in now, you would put them in as separate.” 

How much waste ends up in open waters from Csos depends on the size of collection and storage tanks, as well as how quickly the rainwater fills the sewers. Today, valves in Europe are often used far more than originally intended, in part because green spaces that would have absorbed rainwater have been paved over as cities developed.

Poor maintenance can also result in a build up of fats and oils, which causes sewage to spill over before the rain has a chance to sufficiently dilute it. In the worst cases, undiluted sewage is released when there's no rain, known as “dry day spilling.” A lack of monitoring across Europe makes it hard to know how often these dry spills occur. But data from the UK, which now monitors all of its Csos after public backlash over spills, shows that they’re happening more frequently than previously thought.

Health risks

The effect of this is harmful to both humans and the environment. Untreated wastewater encourages the growth of algae, which chokes other vegetation, depriving animals of the food they need and killing molluscs, which act as natural water filters. Runoff can contain chemicals and microplastics from roads. There’s also the risk of bacteria, such as E.coli and Enterococci, that can make people sick. (The Olympics organising committee said it’s “not aware of any established link” between the athletes’ illnesses and the Seine’s water quality.) Even treated wastewater can vary in quality. In the Baltic Sea, data from Denmark, Finland, Germany, Poland and Sweden show that raw sewage spills are responsible for just 6% of the nitrogen and 16% of the phosphorus from wastewater; most of the rest comes from treatment plants that don’t do a good enough job of scrubbing those nutrients.

But aging sewer and water treatment systems have long been overlooked as a problem. “Some countries don't even know where their Csos are,” says David Butler, a professor of water engineering at the University of Exeter in the UK. The new EU regulations aim to change that, with a requirement for companies to monitor how often their systems spill. “I think we’re going to see in the future some big surprises coming through from our European compatriots,” Butler says.

Polish Prime Minister Donald Tusk is a rare politician who’s put water pollution front and centre — at least in his rhetoric. In his first official speech in December, Tusk pledged to clean up the Oder River, the country’s second-longest waterway, which has been sullied by harmful saline from coal mines, raw sewage and agriculture waste. As many as 90% of sewers in Poland are Csos, among the highest levels in Europe.

Dead fish

The situation came to a head in 2022 when “several hundred kilogrammes of dead fish were fished out of the canal” every day, says Ewa Sternal, who owns a marina along the Gliwice Canal which connects to the Oder River. “[They] looked like they had been electrocuted.” The headlines were bad for business, says Sternal, who spent more than a decade helping to turn the former industrial site into a tourist attraction.

Despite his promises, Tusk has faced criticism for not doing enough. Dead fish still show up in the Oder and saline levels are often high. The government has set up a river clean-up and monitoring taskforce comprised of several ministers, the climate ministry said in response to questions. The infrastructure ministry is also seeking to tighten control over permits mines need to dump wastewater into rivers.

Countries across the region will have to embrace that all-of-government approach if they want to fix their dirty waterways. Many cities increasingly favour using urban planning to slow the flow of rainwater into the sewers. 

In Copenhagen, officials have created “rain gardens” to absorb rainfall and curb flash flooding.

It’s an approach that’s much cheaper, and less disruptive, than the only foolproof solution: separating the existing CSOs. Cost estimates for doing so in the UK, for example, range from £350 billion to £600 billion, which Chisholm from the Chartered Institution of Water and Environmental Management called “clearly unrealistic.”

But making public spaces more flood-resistant requires buy-in from multiple agencies, from housing departments to road and rail agencies, which isn’t easy to achieve when there’s little public pressure to make those changes. Raising awareness is a huge challenge, says Pieter Elsen, founder of the environmental group City to Ocean in Brussels. Belgium’s sewer network has the highest share of CSOs in Europe, according to Moody’s, yet Elsen has struggled to get people to care about the risk that poses to his city’s canals.

“I want to be proud of my own city,” says Elsen, who wants Brussels to introduce more green spaces and build more basins to store rainwater. His group organises kayak trips so people can see the pollution up close, and campaigns for measures like trash barriers to make it easier to take plastic waste out of the water. “If you see that your canal and your river is every month, several times, polluted by your own sewage, it's not something to be proud of.”

On a wet, gray day in June, Nÿs, the Ghent resident, joined hundreds of people piloting blow-up boats, paddleboards and even a wooden house-boat at a floating protest. A DJ played disco tunes as campaigners from Waterland, the group that organized the event, talked to people about the causes of pollution in the city’s canals.

Waterland’s goal is to change people’s view of water — making it something that they enjoy, value and take pride in. As well as conducting water testing and pushing the government to create more green spaces, it runs poetic and historical walking tours on the canals. “It's a kind of cultural switch that we have to make,” says Lieven Symons, the coordinator of Waterland.

In Ghent, homes used to eject their waste water directly into the canals; it’s still possible to see the pipes dotted along the walls. Some homes, especially outside the city, continue to do this. There are 8,000 Csos in the wider region of Flanders that surrounds Ghent. As of last year, less than 10% were being monitored.

Katrijn Van den Broeck, who works on Flanders’ sewage systems at the publicly-owned water company Aquafin and also volunteers for Waterland, says there are too many other priorities to move quickly. Aquafin gets around €150 million a year to spend on new projects in Flanders, including separating Csos and connecting houses to the sewer system. “It’s very high cost, and there are so many places,” she says. “It’s not as easy as it seems.”

But for residents who live by these waterways, it’s a shame to watch them contaminated by sewage. Freya Peeters, 43, runs a canal-side bar in Ghent. She’s been wary about swimming and kayaking in the river near her home after picking up E.coli from a river in Spain. And she’s seen dirty water from her neighbors' homes pouring directly into the river where she lives. A colleague once picked up a serious illness from swimming in the Ghent canal.

Cleaner water would help her attract more customers. “Where you can swim, it’s a place to meet,” she says. But, more importantly, the current situation just isn’t tenable, she says. “It’s not safe.”

Bloomberg