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 bathable by 2025, and the Games served as a huge boost, even though some sporting events were canceled 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 adviser 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 wastewater 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 rainwater 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.
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 preindustrial era," Lavaud said. "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?
"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 nonstop for two weeks, it could be difficult."
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 our partners about this," Lavaud said, referring to the international sporting federations.
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.
"There are always risks [that 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 $1.53 billion project of the Austerlitz basin that will be completed in April.