During the Paris 2024 Olympic Games, global attention turned to the River Seine, an iconic waterway chosen to host open-water swimming events. As athletes prepared to compete, concerns around water quality became increasingly prominent. The most recent samples taken at several strategic locations, including near Pont Alexandre III and the Bercy basin, raised serious questions.
With elevated levels of intestinal enterococci, Escherichia coli, and other bacteria, uncertainty grew over whether pollution thresholds complied with European standards. Unsettled weather in the weeks leading up to the events, marked by heavy storms, further intensified concerns among public authorities and environmental organisations.
Following the closing ceremony on Sunday 11 August, new information began to emerge. Contrary to official reassurances from the Olympic Organising Committee, investigative reporting suggested that water quality in the Seine was, at times, insufficient. This raised an important question: what were the real health risks?
What are the risks of poor water quality?
When water quality is assessed for bathing or sporting events, analysts focus primarily on levels of Escherichia coli and enterococci. These bacteria significantly degrade water quality when present in excessive amounts. Athletes exposed to such conditions risk gastrointestinal illness or skin infections.
Swimmer’s itch (cercarial dermatitis) typically presents as intense itching and skin irritation after contact with contaminated water. It often occurs in natural watercourses inhabited by aquatic birds and freshwater snails. Another risk cannot be ignored: leptospirosis, a bacterial disease associated with rodent contamination, can cause vomiting, high fever, headaches and diarrhoea.
Contamination levels tend to rise after heavy rainfall, as intense storms can overwhelm wastewater treatment systems. Untreated wastewater may then be discharged into the river, a phenomenon observed shortly before the start of the Games.
| Illness | Symptoms |
| Gastroenteritis | Diarrhoea, vomiting, abdominal pain, fever |
| Swimmer’s itch | Itching, rashes, redness |
| Leptospirosis | High fever, headaches, vomiting, diarrhoea, muscle pain, chills |
The cost of making the Seine “safe to swim”
In 2015, a large-scale river clean-up programme was launched with a budget of €1.4 billion. Funding came from multiple public bodies, including regional authorities, the City of Paris, and water management agencies.
In parallel, upstream infrastructure was upgraded to meet environmental standards along both the Seine and the Marne. One example is the Austerlitz retention basin, built at a cost of €100 million to absorb excess rainfall. The structure is designed to prevent overflow during storms.
An 8.8 km wastewater collector was also constructed between Athis-Mons and Valenton, representing an additional investment of €300 million.
Official water quality analysis results
According to information obtained by investigative journalists, internal laboratory reports linked to the Paris municipality painted a troubling picture: water quality was deemed suitable for swimming only around 20% of the time during the Games.
- Since the start of the Olympics, water quality thresholds set by World Triathlon were met on just two days.
- On 3 August, E. coli levels exceeded recommended limits.
- Triathlon events were held on 31 July despite variable conditions.
- Training sessions were repeatedly postponed due to unsatisfactory water quality.
On 5 August, athletes reportedly competed in water that did not meet safety standards. Access to detailed analysis results has since become increasingly restricted, with regular public reporting suspended.
Athletes were informed of the risks
Organisers stated that athletes were given access to water quality data prior to competing. According to these accounts, participants did not refuse to race, even when some results exceeded recommended thresholds.
Several athletes reported illness after swimming
Despite assurances, multiple athletes later reported symptoms consistent with waterborne illness. One competitor publicly stated: “I vomited repeatedly and suffered from diarrhoea.”
Other swimmers reported nausea and gastrointestinal distress following open-water events. Although officials maintained that competitions were authorised based on available analyses, doubts persisted.
Another athlete described ingesting river water and witnessing conditions that raised serious concerns about long-term cleanliness and safety.
Beyond the Olympic Games, plans remain to open designated swimming areas for residents and visitors in future summers. These sites would be supervised, clearly marked, and equipped with changing and shower facilities.
Lingering doubts remain
Plans to host swimming events in the Seine date back over a decade. While infrastructure improvements have been substantial, the river’s long history of pollution continues to cast doubt on claims that it is consistently safe for bathing.
Heavy rainfall still carries hydrocarbons and heavy metals into the river system. Given the illnesses reported and the limited transparency around testing data, uncertainty remains.
It is also worth remembering that the water we consume can expose us to similar health risks if it is not properly treated. This is why effective household water filtration matters. Weeplow offers a gravity-fed water filtration system capable of removing over 99% of harmful bacteria. You may not choose to swim in the Seine, but you can at least ensure the water you drink at home is clean and safe.
