Anne Hidalgo, the Mayor of Paris and a staunch supporter of green initiatives, who postponed her historic dip in the Seine due to the early legislative elections, will finally bathe during the week of 15 July.

The Seine will be the venue for the Paris 2024 10km open water swimming and triathlon swimming events at the Olympic and Paralympic Games, provided that pollution in the river that runs through much of France and the capital can be sufficiently reduced.For decades, the Seine has been toxic to marine life and swimmers, used only for the transport of goods and tourist cruises.

It has also become a dumping ground for unused bicycles and other rubbish. Swimming in the Seine has been illegal since 1923, just one year before the second Olympic Games were held in Paris.

In early April, the Surfrider Foundation claimed to have analysed laboratory tests and concluded that the water in the Seine, which stretches nearly 800 kilometres across France, remains contaminated and potentially dangerous in the Paris area, where the Olympic swimming events will be held.

While efforts are being made to treat the Seine using various methods, including the construction of a huge storage basin (the equivalent of 20 Olympic-sized swimming pools of dirty water to be treated rather than released into the river) to reduce the need to discharge sewage into the Seine when it rains, the results have not been satisfactory from a bacteriological point of view.

As part of the launch of the clean-up plan, Hidalgo had invited high-ranking officials to swim in the Seine in an event dubbed "the big dive", including President Emmanuel Macron himself, who had also promised to swim in the iconic French river.

The cost of cleaning up the Seine is estimated at €1.4 billion, funded by the national government and the capital's authorities.

New infrastructure to absorb heavy rainfall, including the 50,000m3 Austerlitz reservoir, is expected to help reduce undesirable levels of bacteria that can cause serious health problems for competitors and the general public. However, this may not be enough in the event of heavy rainfall in the French capital, which could lead to the suspension, postponement or even cancellation of events on the Seine.

The Olympic events (26 July to 11 August) are scheduled to take place there, but are still at risk in the event of heavy rainfall, which would increase pollution levels, making it unsafe for athletes to swim and indicating that pollution remains unresolved.