PARIS (AP) — Heavy rains have set back plans to test Paris’ readiness for swimmers to race in the River Seine at next year’s Summer Olympics, but Games organisers say the waterway will be better prepared in 2024.

The Open Water Swimming World Cup event was postponed for at least 24 hours because of unacceptable water quality caused by several days of rain, organisers said Friday. That means the women’s race was pushed back from Saturday to Sunday, when a men’s race was also scheduled.

“The water quality in the river Seine is still below acceptable standards for safeguarding swimmers’ health, following several days of rainfall,” the French Swimming Federation (FFN) said in a statement. “As a result, the decision has been taken, in consultation with public health authorities and event delivery partners, to modify the proposed schedule.”

Earlier Friday, organisers cancelled a planned training session for swimmers aiming to compete this weekend in the river that cuts through Paris, after swimming’s international governing body also said the water quality was below acceptable standards.

That can happen when rains cause overflows of untreated waste into the Seine. France’s capital city is spending massively on water-management projects that officials say will make pollution caused by storms less frequent.

The open competition is among a raft of events being used to test Paris’ Olympic plans. The Seine is the venue for marathon swimming at the Games next summer and the swimming leg of Olympic and Paralympic triathlon.

Games organisers said in a statement Friday that water quality will be improved next year when additional infrastructure to better manage rains and wastewater comes online. Those public works include a giant underground reservoir in Paris that will stock excess water during storms, so it doesn’t have to be spilled untreated into the river and can be treated later.

They also say the schedule for Olympic events in the river can be adjusted next year if the water quality doesn’t allow them to take place on their original dates.

Their statement said the recent weather that pushed the Seine below acceptable levels was “exceptional,” with the Paris region seeing its heaviest summer rainfalls in 20 years.