How clean is the Seine and can it really be used for Paris Olympics outdoor swim events?

How clean is the Seine and can it really be used for Paris Olympics outdoor swim events?
Swimmers flout the ban on swimming in the Seine in Paris during the 1946 heatwave. Photo: AFP
Three years until the Paris Olympics - and 33 years after then-President Jacques Chirac promised to transform the then-filthy Seine - how clean is the river that runs through the French capital?

Olympic open water swimming events are scheduled to take place at the Pont d’Iéna, in the shadow of the Eiffel Tower – which means the pressure is on to ensure that the water quality is good enough. And it is the big question at the LH forum in Le Havre, which opens today, where the state of the river will be a key topic on the agenda.

And the news is promising, but there is still much to do, according to officials.

Unlike Chirac, for whom a dip in the Seine in 1988 would have been insane, Arthur Germain – the son of Paris mayor and presidential candidate Anne Hidalgo – swam the 800km length of the river this summer while wearing equipment to test water quality in real time. 

He told Le Parisien that his Seine swim lasted 50 days, and that he finished it ‘without having the slightest pimple or stomach ache’, adding that water quality in the river across the Île de France region was better than researchers had expected.

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Since the 1970s a number of fish species have returned to the river as water treatment works have improved, increasing oxygen levels in the water.

“There were three species of fish … there are now more than 30,” said Christophe Poupart of the Agence de l’Eau Seine-Normandie (AESN), responsible for monitoring the state of the river and its basin. 

But pesticide pollution remains a serious problem, he said. “Between 2013 and 2019, the number of rivers poisoned by nitrates has doubled.” 

Ecological pressure on the river is massive, according to Poupart. About 30 percent of the population of France live near the Seine, the smallest of the four major French rivers. 

Despite that, Dan Angelescu, founder of Fluidion which measures bacteria levels under the Alexandre-III bridge in Paris, said: “We see signs of improvement, the quality of bathing water could be satisfactory even in Paris. But it will require close monitoring.”

Swimming in the river in Paris has been illegal since 1923. 

Further along the river, towards the estuary, conditions aren’t quite so promising – in part because of the heavy industry along the river in Normandy.

“France has five major plastic producers, two of which are located on the Normandy Seine. As a result, we find about 1 million tons per year in the estuary,” ecologist Laurent Colasse said. 

Environmental associations have cleaned up waste plastic dating back to the 1970s and 1980s along the banks of the river in Normandy. Romain Tramoy, a researcher at the École des ponts at the University of Paris-Est-Créteil, described the waste ‘like fossils but with the advantage of having the date engraved … Many go back 40-50 years’.

The Paris Olympic organising committee want to hold outdoor swimming events such as the triathlon in the Seine – at present the Paris triathlon uses the slightly cleaner waters of the Canal Ourcq which runs through the north of the city.


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