PARIS (AP) — French officials inaugurated on Thursday a huge water storage basin meant to help clean up the River Seine, set to be the venue for marathon swimming at the Paris Games and the swimming leg of the Olympic and Paralympic triathlons.

Sports minister Amélie Oudéa-Castéra praised Paris’ ability “to provide athletes from all over the world with an exceptional setting on the Seine for their events.”

Last year, swimming test events had to be canceled due to poor water quality. One reason was heavy rains that overwhelmed the city’s old sewers, causing a mix of rainwater and untreated sewage to flow into the Seine and leaving safety standards unmet.

The giant reservoir dug next to Paris’ Austerlitz train station aims to collect excess rainwater and prevent bacteria-laden wastewater from entering the Seine.

It can hold the equivalent of 20 Olympic swimming pools of dirty water that will now be treated rather than being spat raw through storm drains into the river.