A French water charity sounded the alarm Monday about pollution in the river Seine, which is set to be used for swimming during the Olympic Games, reports FRANCE 24.
Surfrider Foundation said it had analysed six months of tests undertaken by a laboratory and had concluded that the river water remained polluted and potentially dangerous.
In an open letter, the Biarritz-based charity said it "wanted to share with stakeholders its rising concerns about the quality of the Seine but also the risks faced by athletes moving in contaminated water".
Paris authorities are in a race against time to clean up the Seine before the start of the Olympics on July 26, with the famed waterway set to play a starring role during the Games.
It is set to be the host of the opening ceremony and will then be used for the marathon swimming events and the triathlon -- pollution permitting.
Around 1.4 billion euros ($1.5 billion) has been spent upgrading sewage and storm water treatment facilities in the Paris region over the last decade to improve the quality of the Seine as well as its main tributary, the Marne.
A major new storm water facility is expected to be inaugurated later this month, while new sewage connections for river boats are continuing to be built.
Surfrider said tests had been carried out by the laboratory Eau de Paris and environmental analysis group Analy-Co from September to March underneath the bridges Alexandre-III and l'Alma, where the Olympics sports are set to take place.