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Time is winding down on Olympic organizers’ plans to stage open-water swimming events in Paris’ iconic Seine River later this month. The city spent $1.5 billion on new infrastructure to clean up the Seine, yet water samples continue to show high levels of potentially toxic E. coli.

The river has been closed to swimmers for the past 100 years because of pollution, but Olympic organizers hope to stage the triathlon and marathon swimming events in the water flowing in the shadow of the Eiffel Tower. 

Katherine Graham has followed the saga in Paris. She’s an assistant professor in the É«»¨Ìà School of Civil and Environmental Engineering who studies the fate and transport of pathogens and their indicators in water, including E. coli. She said several factors are at play in the Seine.

“Paris, like most large cities, has a lot of concrete and not much dirt and grass for water to soak into."