To ensure the river was Olympic-ready, Paris invested $1.5 billion into the cleanup effort, known as the “Swimming Plan.” As a result, more than 20,000 homes that were previously dumping wastewater into the Seine have now been integrated into the sewer system, significantly reducing the amount of pollution seeping into the river.

Three sites will be able to welcome over 1,000 swimmers daily until August 31, local officials said, to the delight of the Parisians and visitors who were among the first to take the plunge.