Paris opened the River Seine to public swimming on 5 July 2025, ending a ban that had been in place since 1923. The decision follows a €1.4 billion water-quality overhaul carried out ahead of the 2024 Olympic Games, when triathlon and marathon-swim events were held in the river. Three supervised sites—Bras-Marie in the 4th arrondissement, Grenelle in the 15th and Bercy in the 12th—now welcome bathers free of charge until 31 August. The areas, equipped with pontoons, showers and lifeguards, can accommodate more than 1,000 swimmers daily; some 2,300 people took the plunge on the first morning. The clean-up connected tens of thousands of homes to the sewer network, upgraded treatment plants and added large storm-water reservoirs to curb sewage overflows. Water quality is tested every day, and a beach-style flag system signals when conditions are safe or unsafe for bathing. Heavy rain on 6 July pushed bacteria levels above safety thresholds, prompting authorities to close the three sites less than 24 hours after the launch. They reopened on 10 July once fresh tests cleared the water, and officials say temporary closures will remain possible after storms while daily monitoring continues.