A quarter of a century after the late president Jacques Chirac promised Parisians they would be able to swim in the Seine within three years, the French capital’s mayor has confirmed three river bathing areas are to open in the city in 2025. The sites – opposite the central Île Saint-Louis in the centre, by the Quai de Grenelle in the 15th arrondissement to the west, and at Bercy in the eastern 12th arrondissement – will be monitored by lifeguards and marked by buoys, Anne Hidalgo said on Sunday. The bathing zones will also be “accessible by pontoons and equipped on the quaysides with spaces where swimmers will be able to change, shower and keep their belongings safe”, the city hall said in a statement. The mayor has said she wants swimming in the Seine to be a “major legacy” of the 2024 Paris Olympics, in which the river is to feature as the scene of the opening ceremony and in three aquatic events, including the triathlon. Hidalgo, who has been mayor of Paris since 2014 and ran as the Socialist party’s presidential candidate in 2022, tweeted a video showing her deputy mayors “taking the first plunge” and promising it would “soon be your turn – and mine”. Bathing in the Seine has been banned since 1923, when the city authorities outlawed the open-bottomed swimming boats that lined the quaysides because of the dangers from barge and pleasure traffic and rapidly deteriorating water quality. However, a €1.4bn clean-up project under way for the past seven years is now bearing fruit, authorities say, with regular tests last year showing waterborne bacteria – notably E coli and enterococci – at a safe level for swimming more than 90% of the time. Only after periods of particularly heavy rainfall is the water quality unacceptable, and then only for a relatively short time, authorities say. Extensive testing will be carried out daily when the river is officially opened for bathing, the city hall has promised. The clean-up has involved cracking down on homes, boats and businesses emptying wastewater into the river, improving sewage treatment plants, and building huge storage basins to stop bacteria-filled wastewater spilling into the river after rain. With Paris facing the prospect of sweltering summer temperatures – potentially climbing to more than 50C by the year 2050 – swimmable waters will also help the French capital be more livable in the future, the council says.