Paris 2024 Olympics: why poor water quality in the Seine could threaten the opening ceremony ?

The opening ceremony is still pending. MAXPPP

Anxious countdown for organizers: the Seine was carrying too much water and bacteria one month before the opening of the Paris Olympic Games (July 26 – 11 ;August), reinforcing doubts about the good holding of the open water events and the opening ceremony.

In the Paris region, the gloomy spring has given way to a start to a summer worthy of the name, dry and sunny. But the precipitation of the last few weeks still has serious hydrological consequences.

The river quality analysis reports published on Friday by the town hall and the regional prefecture, covering the week of June 17 to 23, showed a sharp increase in fecal bacteria concentrations compared to the previous two weeks.

The Escherichia coli and enterococci content must not exceed 1,000 and 400 colony forming units (CFU)/100 ml respectively for the tests to be authorised. While E.Coli concentrations were generally between 1,000 and 5,000 CFU/100 ml in the first half of June, they fluctuated between 2,000 and 10,000 – with a peak of 13,000 – at the beginning of the third week, between 2,000 and 6,000 at the end of the week.

“We expect things to improve this week given the weather”

As for enterococci, with values ​​generally between 100 and 500 CFU/100 ml in the first half of June, they rose above the 1,000 or even 2,000 mark for several days. "Water quality remains degraded due to an unfavorable hydrological context: rain, high flow, little sunshine, temperatures below seasonal standards and pollution from the water. rsquo;amont", summarize the town hall and the prefecture.

"We expect things to improve this week given the weather", commented the regional prefecture to AFP. On Wednesday, prefect Marc Guillaume warned that the river would not be swimmable at the beginning of July. The hour of truth is approaching for the organizers: after the opening ceremony, the Seine must host the triathlon events (July 30 and 31, August 5), swimming- marathon (August 8 and 9) and paratriathlon (September 1 and 2).

The Austerlitz basin was able to function

In case of intense precipitation, untreated water – mixture of rain and wastewater – can be discharged into the river, a phenomenon that retention works inaugurated before the Games are intended to prevent. Town hall and prefecture also emphasize that the rains of June 17 and 18 allowed the Austerlitz basin, inaugurated at the beginning of May, to operate for the first time.

If these works prove insufficient in the event of heavy rain, plan B consists of postponing the tests for a few days, but not changing location. But attention is now focused more on the flow of the Seine, "six times more"higher than usual during the week observed: it was 666 cubic meters/second on Sunday, while it is normally 100 to 150 cubic meters during this period.

Transition times to be respected for the ceremony

It was because of this excessive flow that the rehearsal for the opening ceremony scheduled for Monday was postponed. Although it has since fallen again, it has been stagnating since Thursday at a plateau around 430 m3/s. Not content with threatening the safety of swimmers, a high flow rate is also problematic for the nautical parade of the opening ceremony because it accelerates the speed of the boats, and therefore disrupts the passage times of a precise show.

After the return of rain expected in the first week of July, Météo France indicates "that’no scenario" does not emerge for the last three weeks until the Olympics. The president of the Olympic organizing committee, Tony Estanguet, estimated on Wednesday on France Inter that we will "see clearer in mid-July"< /em>.