The rehearsal was originally scheduled for 24 June but was cancelled because the river was in spate. After several weeks of rainy weather, the flow of the Seine was five times stronger than its normal summer reading.

The flow remains abnormally high. Late on Friday afternoon, after another rainy day in the city, the volume of water still exceeded 500 cubic metres a second which is considerably greater than the usual 100 to 150 cubic metres a second in summer. The Ministry of Sport has said the maximum acceptable flow is "450 cubic meters a second". It said that the boats would simply go down the river too fast.

The Ministry also said such a flow also clouded the chances of satisfying the water quality requirements for marathon swimming and triathlon events scheduled in the Seine. The "very rainy weather" had caused "the strong flow of the river, which does not help to produce a good water quality", Paris city hall said in June.

Thierry Reboul, Director of Ceremonies for the Organising Committee, told AFP last week that at between 300 and 500 cubic meters, the ceremony would have to be "adapted". As an example, he mentioned "removing the tallest boats".

Organisers have built stands for VIPs and ticket holders along the riverside banks and on bridges. They also planned 222,000 free seats on the roads looking down along the higher banks but, said Reboul, had cut 8,600 of these for "security reasons”.

On Saturday, following the rescheduling of the rehearsal, French Sports Minister Amelie Oudea Castera swam in the Seine to demonstrate its cleanliness and suitability for the upcoming Olympic Games.