The quality of the waters of the iconic Parisian river has been called into question on several occasions before and during the Games, and on Sunday one of training sessions was suspended as Belgian triathlete, Claire Michel's condition worsened.

According to the Belgian National Olympic Committee on Sunday, Michel felt unwell after taking part in the women's individual Olympic triathlon on Wednesday.

One of the participants in a complicated event, fellow Belgian Jolien Vermeylen, described the "Sunderland River and the Hong Kong World Cup" as "much worse water to swim in".

"The COIB and Belgian triathlon hope that lessons will be learned for future triathlon competitions at the Olympic Games," the Belgian Olympic Committee warned in the statement. This situation and the suspension of training for the in-water portion of the triathlon casts doubt on the mixed relay event scheduled for Monday. It is not the only event pending on the river: the men's and women's marathon swims are scheduled for 8 and 9 August.

Training in the river was interrupted last week, and the men's individual event was postponed due to pollution problems. Many triathletes were caught by surprise by the strong currents in the Seine, with some expressing concerns about water quality and delays affecting their training and the men's competition.

In this case, Thursday night's heavy storm is suspected to have worsened the water quality of the river, as downpours often cause sewage overflows in the Seine.

However, on Saturday night Paris 2024 spokeswoman Anne Descamps said Sunday's training sessions had also been cancelled, due to the rain in recent days and linking Monday's event to confidence in improved weather forecasts.

The challenge of the quality of the Seine

Paris had set out to make the most of its identity for the Games, presenting itself to the world as a city full of monuments and recognisable symbols. The opening ceremony turned the city into a stage, especially the River Seine, along which the national delegations paraded in boats.

It was also announced that sporting events would be held on the iconic river, raising doubts from citizens and environmental groups about its quality. Sports Minister Amelie Oudea-Castera and  Mayor Anne Hidalgo bathed in the river as a way of sending a message about its good condition.

French authorities have invested 1.4 billion euros ($1.5 billion) over the past decade to clean up the Seine. Paris organisers said the water quality was "very good" according to criteria used by the World Triathlon. Levels of E. coli bacteria, a key indicator of faecal contamination, were recorded at 192-308 colony-forming units per 100 millilitres (cfu/ml) on race day, well below the maximum limit of 1,000 cfu/ml.

Nevertheless, heavy rainfall can overwhelm the city's underground drains and sewage system, causing untreated effluent to be discharged into the river. It has not helped that the weather has also been erratic, ranging from heat waves to torrential rain.