Visitors walk inside the construction site of the 30m-deep Austerlitz basin. GETTY IMAGES

French officials inaugurated a huge water basin in Paris on Thursday, in preparation for the upcoming Olympic and Paralympic Games to be held in the city over the summer.

The new reservoir next to Paris' Austerlitz train station aims to collect excess rainwater and prevent bacteria-laden wastewater from entering the River Seine; the venue for marathon swimming and the swimming leg of the Olympic and Paralympic triathlons, as well as the Games’ opening ceremony

Last year, swimming test events had to be cancelled after heavy rains overwhelmed the city's old sewers, causing a mix of rainwater and untreated sewage to flow into the Seine. With the new basin in place, 20 Olympic swimming pools of dirty water can be stored and treated rather than overflowing into the river. 

The new storage basin "guarantees" that water can be stored even during severe storms, and will help water levels to "return to normal as quickly as possible,” Paris mayor Anne Hildago explained.

During the Olympics, water will be tested daily to determine whether events can go ahead as planned.

Sports minister Amélie Oudéa-Castéra praised the city's ability "to provide athletes from all over the world with an exceptional setting on the Seine for their events".

Tony Estanguet, Paris 2024 President, says they are not doing it just for the Games.

"The Games were just a pretext. An accelerator," Estanguet said in an interview with the press. "Games that are at the service of the territory, at the service of the inhabitants, and at the service of the environment too. Because it will be less pollution."

The opening of the water basin is part of a series of facilities being built to clean up the Seine, including a water treatment plant east of Paris inaugurated last month. Paris officials also plan to open several bathing sites to the general public in the summer.