“Paris 2024 and World Triathlon reiterate that the priority is the health of the athletes. The analysis carried out yesterday in the Seine showed water quality levels that … do not present sufficient guarantees to allow the event to take place,” the statement said.

Organisers blamed rain in recent days and said they were “confident” water quality would improve enough before the triathlon competition is due to start on Jul 30.

In the event of heavy rain, untreated sewage can be washed into the river.

If the quality is below standards a “Plan B” involves postponing the events for a few days or moving the marathon swimming to Vaires-sur-Marne, on the Marne river east of Paris.

On Jul 17, Paris Mayor Anne Hidalgo swam in the Seine along with Paris 2024 chief organiser Tony Estanguet.