A view shows an aerial subway and the construction site of the Austerlitz basin, an underground water storage reservoir for wastewater and rainwater, build to improve the sanitary quality of the water in the Seine River, ahead of the Paris 2024 Olympics, in Paris, France, Nov 29, 2023. (PHOTO / REUTERS)

PARIS - The River Seine is already suitable for bathing two days out of three on average in the summer, but Paris is hoping to further improve the water quality as next year's Olympics loom.

The primary goal is to make the Seine batheable by 2025, and the Games served as a huge boost, even though some sporting events were cancelled last summer because the health standards were not met following rare heavy rains and a sewer problem.

"The amounts of rain we had had not been (seen) since the 1970s," Pauline Lavaud, the Paris mayor's advisor on energy and climate transition, water and maintenance of public spaces, told reporters.

The city has been building a storage basin capable of holding 46,000 cubic meters of waste water to significantly reduce the risks of pollution of the Seine

The city has been building a storage basin capable of holding 46,000 cubic meters of waste water to significantly reduce the risks of pollution of the Seine.

The water will be tested every day during the Olympics to make sure it will be safe for athletes and triathletes to swim in the Seine.

Once the rain water is collected in the Austerlitz basin - a monster, 30-meter deep structure the size of a dozen Olympic swimming pools - it will be evacuated through a tunnel beneath the train station to a treatment plant.

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A worker stands in a giant tunnel built to allow water to flow into the tank at the construction site of the Austerlitz basin, an underground water storage reservoir for wastewater and rainwater, build to improve the sanitary quality of the water in the Seine River, ahead of the Paris 2024 Olympics, in Paris, France, Nov 29, 2023. (PHOTO / REUTERS)

When the water meets the required health criteria, it will then be poured into the Seine.

"We are now back to the level of sanity of the pre-industrial era," Lavaud said.

Benjamin Raigneau, the city's Cleanliness and Water director, said that after only two types of fish could be found in the river in the 1980s, there were now more than 30, including crayfish

"The Olympics have made us gain 10 years on our project of making the Seine bathable."

Benjamin Raigneau, the city's Cleanliness and Water director, said that after only two types of fish could be found in the river in the 1980s, there were now more than 30, including crayfish.

Will it be enough, however, for the open water and triathlon events to take place?

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"We're trying to reduce all risks, and if it is not possible to swim one day, the events can be postponed," Lavaud said.

"If it rains non stop for two weeks, it could be difficult."

Employees work at the construction site of the Austerlitz basin, an underground water storage reservoir for wastewater and rainwater, build to improve the sanitary quality of the water in the Seine River, ahead of the Paris 2024 Olympics, in Paris, France, Nov 29, 2023. (PHOTO / REUTERS)

Controls will be increased as the Games approach, with all boats needing by law to be linked to the sewage system.

Transparency will also be key and Paris officials have yet to pledge they will make the water quality data accessible, although they did not rule out they would publish them.

"We need to discuss with out partners about this," Lavaud said, referring to the international sporting federations.

A technician takes a sample of water from the Seine River to perform bacteriological analysis near the Alexandre III bridge in Paris, France, May 31, 2023. (PHOTO / REUTERS)

Former Paris mayor Jacques Chirac in 1988 promised he would swim in the Seine "in the presence of witnesses". Current mayor Anne Hidalgo is about to make that dream come true, although any mishap during the Olympics would be seen as a setback.

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"There are always risks (than the Seine will not be bathable on the days of Olympic events). But the legacy will be delivered," said Samuel Colin-Canivez, who is leading the 1.4 billion-euro ($1.53 billion) project of the Austerlitz basin that will be completed in April next year.