Formulated in 1990, the promise of Jacques Chirac, then mayor of Paris, to bathe "within three years" in the Seine has never been kept.

But three decades later, the State, the City of Paris and other local authorities, from all political stripes, have injected around 1.4 billion euros into a "bathing plan" in order to "realize this dream", according to the expression of the current mayor Anne Hidalgo.

Disputed between the Invalides and the Eiffel Tower, the open water swimming and triathlon events should mark a new start in relations between the general public and the river, which has been prohibited for swimming for a century (1923).

The opening of around twenty bathing areas in Île-de-France is planned in the years to come.

In Paris itself, four sites are under study.

The number and location of these "stations" will be defined "as a legacy of the Games, by the end of 2024", said Amélie Oudéa-Castéra, the Minister of Sports and the Olympics, at the end of February while visiting the station. depollution of rainwater in Champigny-sur-Marne (Val-de-Marne).

In this town in the east of Paris which still had a crowded beach in the 1960s, according to an archive photo, this 45 million euro project should allow retention and ultraviolet treatment before discharge into the Marl from rainwater mixed with wastewater.

About 30,000 bad connections

Because this rainwater is polluted upstream by bad connections "of about 30,000 diagnosed households" whose waste water "goes directly into the Marne or the Seine", summarizes François-Marie Didier, the president of the interdepartmental union for sanitation in the Paris area (Siaap).

Preventing this cocktail from soiling the river is also the objective of the Austerlitz storage basin, built near the Parisian station so that "the sewers do not overflow", summarizes the deputy in charge of the Olympic Games and the Seine, Pierre Rabadan.

The development, for 264 million euros, of the VL8 collector, in the south of the Paris conurbation, is also part of the efforts to improve sanitation, as is the painstaking work of supporting individuals to correct their bad connections.

In the Val-de-Marne, "we must be at a good half" of individuals now well connected, estimates the president of the department Olivier Capitanio.

The prefecture of Ile-de-France (Prif), which oversees the bathing plan with the City of Paris, has the objective of “erasing three quarters of the pollution by 2024” linked to bad connections.

"If we reach this objective of 75%, it must be possible to swim in the Seine", adds the Prif.

Based on a 2006 European directive, the regulations require the microbiological analysis of two faecal bacteria, Escherichia coli and intestinal enterococci.

"Last summer, all the daily samples were satisfactory or excellent 7 days out of 10. And that's before all the work in progress", underlines Pierre Rabadan, for whom the proportion rose to 92% on the Olympic period, between the end of July and the beginning of August.

The deputy, however, does not exclude "hazards" such as heavy storms which would lead to discharges of polluted water.

In this case, the organizers have "two-three days of margin" to shift the events, he says.

"We must hope that it does not rain at all in the three days before the Olympics", says Françoise Lucas, researcher in microbiology at the University of Paris-Est Créteil.

However, the summer of 2021 “was very humid”, she recalls.

34 species of fish

Michel Riottot, honorary president of the France Nature Environnement (FNE) Île-de-France association, is very skeptical of the performic acid treatment developed in Valenton (Val-de-Marne), one of the two Siaap wastewater treatment plants upstream of Paris, fearing "massive destruction in the ecosystem" if the acid were to escape.

This treatment is "much more effective than chemical disinfectants", replies the Siaap, which recalls that "ammonium discharges, the main pollution parameter, have been divided by 20 since 1997".

Result, "there are 34 species of fish in the Seine and 37 in the Marne, while there were 3 in the 1990s", welcomes its president, François-Marie Didier.

As for leptospira, another potentially deadly bacterium, "cases of transmission remain limited" and "there is no more risk in the Seine than elsewhere", estimates the National Reference Center for Leptospirosis, based in Paris. 'Pastor Institute.

"This should therefore not impact the conduct of the Games", concludes the laboratory.

© 2023 AFP