An open water swimming test event scheduled for next week in the Seine has been cancelled due to heavy rainfall, the French capital’s authorities said on Friday, June 7.

During this year’s Olympic Games, triathlon and open water competitions will take place in the river. Heavy rainfall can lead to increased pollution in the Seine with officials warning it could overwhelm Paris’ sewerage system.

The discharge in the Seine before Monday’s now-scrapped event was measured at 349 cubic square metres per second, with the level desired for this summer’s events at 100 cubic square metres.

Although a new water treatment plant was inaugurated upstream of Paris at the end of April, another major Olympics-related water infrastructure project has yet to enter service. A giant new underground stormwater facility close to the Austerlitz train station in eastern Paris, which will stock water to prevent discharges into the river, is scheduled to come on stream in early June.

Cleaning up the river Seine is seen as one of the key legacy achievements of the Games, with Mayor Anne Hidalgo promising three public bathing spots for locals next year.

Around €1.4 billion ($1.5 billion) has been spent by French authorities upgrading sewage treatment and stormwater facilities around Paris to reduce the amount of untreated faecal matter flowing into the river and its main tributary, the Marne.