A planned training session Friday for swimmers aiming to compete this weekend in the river that cuts through Paris was canceled because the water quality dropped below acceptable standards, the international governing body of swimming announced.

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.

World Aquatics said in a statement that after days of rains, “the water quality in the Seine has currently fallen below acceptable standards for safeguarding swimmers’ health.”

A decision on whether the Open Water Swimming World Cup event goes ahead as scheduled Saturday and Sunday will follow more water-quality tests, it said.

The 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 organizers 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.

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.

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