Parisians rushed for a dip in the Seine as the authorities opened the river to public swimming for the first time since 1923 after an extensive clean-up operation spurred on by it being used as a venue in the Paris Olympics.
Three sites along the banks of the Seine in the city will be able to welcome over 1,000 swimmers daily until 31 August, local officials said.
"We're especially happy to have proved the sceptics wrong and to be able to deliver on the commitments we initially made, on something that was very big and very complicated to achieve," said Pierre Rabadan, Paris deputy mayor for the Seine river.
The reopening of the Seine for public swimming follows efforts by authorities to improve its water quality so it could be used for Olympic events last summer.
Investments included connecting tens of thousands of homes to the sewer system, upgrading water treatment facilities, and constructing large rainwater storage reservoirs to prevent sewer overflow during heavy storms.
While delays, triggered by the health impact of heavy rains, impacted some Olympic training sessions and the men's triathlon event, competitions in the Seine eventually went ahead, bolstering confidence in the river's safety for public swimming.
Daily water quality tests will be conducted during the swimming season, with green and red flags - similar to beach safety systems - indicating whether swimming areas are open or closed.
"Obviously, if we open the swimming area it is because the water complies with the regulations, it poses absolutely no danger to the people who go swimming," Mr Rabadan said.
As well as the three sites within Paris, 14 swimming areas outside the capital's boundaries will be set up on the Seine and the Marne rivers.
Two of those already opened on the Marne in June.
