Olympic organisers have cancelled a second day of triathlon training on the Seine scheduled for Monday morning after weekend rain in Paris contaminated the waterway that runs through the French capital, the planned venue for the triathlon and open water marathon events.

Despite the second cancellation of training sessions, organisers remain confident that the medal events will go ahead as planned.

In a joint statement, the Paris 2024 organisers and World Triathlon said they had decided to cancel Monday's swim training session because "water quality levels ... do not provide sufficient guarantees" for it to take place. The triathlon is the first Olympic event to be held on the Seine, followed by the marathon swim in the second week of the Games.

A swim training session scheduled for Sunday was also cancelled due to pollution levels, although French officials played down the issue, claiming that the current levels were better than in previous years when competitions were held on the Seine. In particular, they stated that "French athletes are not afraid to compete in the Seine".

The men's individual triathlon is scheduled to start at 08:00 (CEST) on Tuesday, with the women's individual triathlon taking place at the same time on Wednesday, weather permitting, or rather, if the pollution levels remain within acceptable limits for human health without compromising the safety of the swimmers.

The quality of the water in the Seine depends on the amount of rainfall in and around Paris.Although a massive clean-up plan costing nearly 1.4 billion euros has improved the river, heavy rainfall still makes the water unfit.

Heavy downpours, such as Friday's during the soggy opening ceremony of the Games, overwhelm the city's sewage system, causing untreated sewage to flow into the river and increasing bacteria levels.

The weather forecast for France is for sunny conditions on the Monday and Tuesday leading up to the competition, but rain is expected to start again on Tuesday night and continue throughout Wednesday, which could further complicate matters.

Organisers believe that if the days are sunny and there is no rain, the water quality will improve and the triathlon will be able to go ahead as planned. However, if it rains on Tuesday night and throughout Wednesday morning, the bacteria levels could worsen, possibly leading to the cancellation of the women's swim on Wednesday.

Due to an exceptionally wet spring and early summer, the Seine had consistently failed water quality tests until early July. Levels of E. coli bacteria, an indicator of faecal matter, were more than 10 times the permitted limit.

Paris 2024 organisers have the option of postponing outdoor swimming events by several days in the event of rain, but not the triathlon.

As a last resort, they have said they will cancel the swimming leg of the triathlon and move the marathon swim to Vaires-sur-Marne, on the Marne River east of Paris, where Paris 2024 will host the rowing and canoeing disciplines of the Olympic and Paralympic Games.

On 17 July, the Mayor of Paris, Anne Hidalgo, swam in the Seine alongside Paris 2024 chief organiser Tony Estanguet and nearly 100 other people to demonstrate that the river was ready for the Olympic Games, a claim now contradicted by scientific and laboratory results, at least during periods of rain in Paris and the surrounding area.