The City of Paris tweeted that three floating pools on the Canal de l'Ourcq were closed on Monday because the water quality was “unsatisfactory”.
The authorities have since said the pool will re-open on Tuesday.
The cause of the pollution was not clear.
French radio said heavy rainfall over the weekend had led to higher than normal levels of enterococci, a bacteria found in fecal matter.
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Photo: The Local
The pools, which can take up to 300 bathers at a time, are the culmination of a 10-year effort by the City of Paris to purify the canal water so that those who cannot afford a seaside holiday can still take the plunge.
With temperatures last week rising well above 30 degrees Celsius (86 degrees Fahrenheit), they proved an instant hit as hundreds of people queued on the first day for a dip.
Inaugurating the facility, Mayor Anne Hidalgo called it “a dream come true”.
But for most Parisians, being able to swim in the Seine river, past the Eiffel Tower, represents the ultimate prize.
Hidalgo has set a target of 2024, when the city hopes to host the summer Olympics, to have bathers bobbing in the Seine.