One month before the opening ceremony, the Seine is still not ready

The fault lies in a gloomy spring in Île-de-France and heavy rainfall in recent weeks. The river quality analysis reports published on Friday, June 28 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.

Moment of truth

The levels of Escherichia coli and enterococci easily exceed the ceilings to be reached for the tests to be authorized. “We expect things to improve this week given the weather,” commented the regional prefecture. On Wednesday, the prefect Marc Guillaume had already warned that the river would not be swimmable at the beginning of July.

The moment of truth is approaching for the organizers: after the opening ceremony, the Seine must host the triathlon events (July 30 and 31, August 5), marathon swimming (August 8 and 9) and paratriathlon (August 1^is and September 2). In the event of intense precipitation, untreated water – a mixture of rain and wastewater – can be released 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 the location.

Problematic flow rate

The main concern, however, is the flow of the Seine, “six times higher” than usual during the week observed: it was 666 cubic meters/second last Sunday, while it is normally 100 to 150 cubic meters in this period. It is because of this excessive flow that the rehearsal for the opening ceremony scheduled for last week was postponed. Although it has since gone down, it has stagnated since Thursday at a plateau around 430 m^³/s. Not only does a high flow threaten the safety of swimmers, it is also problematic for the nautical parade of the opening ceremony because it increases the speed of the boats and therefore disrupts the passage times of a carefully timed show.