Paris spent a century and 1.4 billion euros making the Seine swimmable again
Swimming in the Seine was banned in 1923 because the water was too dirty. By 1970 so much raw sewage poured in that only three fish species survived near Paris. Today more than 30 live there, salmon have returned, and in July 2025 Parisians were finally allowed back in.
The river runs 777 kilometres from a spring about 30 kilometres northwest of Dijon to the English Channel at Le Havre. Paris has owned that source since 1864 and dressed it with an artificial grotto and a nymph statue, on ground where a Gallo-Roman temple once stood. Offerings to the river goddess Sequana were found there, and her name probably shares an ancient root meaning to flow, rather than the Latin word for follow.
Because Paris sits only 24 metres above sea level yet lies 446 kilometres from the mouth, the current is gentle and easy to navigate; ocean-going ships reach Rouen, 120 kilometres inland. Locks built in the 1800s deepened the once-shallow city channel to about 9.5 metres, and four reservoirs added since 1950 steady the level. They cannot stop extreme floods like January 1910 or January 2018, when the river peaked at 5.84 metres. After a 2003 alert, some 100,000 artworks were evacuated from underground storage, the largest such move since the Second World War.
Pollution is the other long story. Nineteenth-century Paris combined street runoff and sewage in one drainage network, so heavy rain still flushes untreated waste into the river. Toxic discharges from factories went largely ignored until the late 1980s, and nitrogen fertilisers worsened farm runoff from the 1960s. Treatment plants and European water rules in the early 2000s cut phosphorus and ammonium sharply, and Atlantic salmon reappeared in 2009.
Jacques Chirac first urged lifting the swimming ban as mayor in 1988. The Swimming Plan of 2018 built a basin to hold storm water before releasing it slowly into the sewers, aiming at the 2024 Olympics. Mayor Anne Hidalgo swam in July 2024, though E. coli counts often remained too high, and rain during the opening ceremony pushed the triathlon back a day.
Source: Seine
