The Seine was suitable for swimming six days out of seven between July 17-23, data showed on the day of the Paris Olympics opening ceremony on Friday.
Data published by the city and regional authorities showed the concentrations of enterococci and E.coli bacteria were above legal thresholds on July 21.
The French capital has been working on cleaning up the Seine so people can swim in it again, as was the case during the 1900 Paris Olympics. But a sewer problem last summer led to the cancellation of a pre-Olympics swimming event.
The triathlon and marathon swimming legs of the Olympics, which run from July 26
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