PARIS, France (AFP) — The Paris Olympics men’s triathlon was postponed just hours before it was due to get under way on Tuesday after water quality tests on the River Seine revealed it was still too dirty for swimming, organisers said.

In a move that left some athletes angry and Olympic officials scrambling, organisers announced shortly before 5:00 am (0300 GMT) that the men’s event would be delayed by 24 hours.

A joint statement from Paris 2024 and World Triathlon blamed heavy rain on Friday and Saturday, while forecasts of fresh storms later on Tuesday cast doubt on whether any outdoor swimming will be possible this week.

“Paris 2024 and World Triathlon reiterate that their priority is the health of the athletes,” the statement said after a meeting held at 3:30 am local time (0130 GMT) on Tuesday.

“Unfortunately, meteorological events beyond our control … can alter water quality and compel us to reschedule the event for health reasons.”

Heavy downpours overwhelm Paris’s underground drains and sewage system, some of which dates back to the 19th century, leading to untreated effluent being released into the waterway.

The postponement calls into question the confidence of Paris 2024 organisers that a public investment of 1.4 billion euros (US$1.5 billion) to clean up the Seine would bear fruit in time for the Olympics.

The river has been placed at the heart of the Paris Games, from the opening ceremony on its waters last Friday to the triathlon and marathon swimming scheduled for this week and next.

If pollution levels remain too high, possibly worsened by major storms heading for Paris later Tuesday, the triathlon will be turned into a duathlon, meaning only running and cycling.

Paris 2024 Sports Director Aurelie Merle and World Triathlon President Marisol Casado remained confident that the men’s race could take place in its rescheduled slot on Wednesday, just after the women’s race.

“We are quite hopeful because you can see the weather conditions have been quite good over the past few days with the return of the sun and the high temperatures, which have a positive impact on the water quality,” Merle told reporters.

Casado said that “at this point, we are quite confident that we will have them (races) tomorrow and then we will be very happy all of us, the first ones the athletes”.

The last race to be turned into a duathlon because of water problems was the Europe Triathlon Championship in Madrid last year, she added.

Tuesday’s weather forecast looked ominous.

National forecaster Meteo France warned about the danger of strong thunderstorms, heavy rain, hail and lightning from 6:00 pm (1600 GMT) over the French capital which could be accompanied by “intense precipitation”.

Around 25 mm (one inch) of rain fell on Friday and Saturday, the equivalent of the average rainfall for the whole of July, according to Merle.

Another 20-40 mm could fall in less than an hour on Tuesday, Meteo France said.

Benjamin Maze, the technical director of the French Triathlon Federation, told FranceInfo radio that there was “a bit of anger” among competitors when they heard the news of the postponement on Tuesday morning.

“The athletes got up a bit before 4:00 am, they were having breakfast when we received the information from the international federation,” he said. “Obviously there’s a bit of anger and a lot of disappointment.”

Three out of four tests on the river showed E Coli bacteria — a key indicator of sewage — above the upper limits set for triathletes of 1,000 colony-forming units per 100 millilitres (cfu/ml).

The worst reading was 1,553 cfu/ml, Merle said.

The Seine is set to be used for the Triathlon mixed relay on August 5 and then again for marathon swimming — a 10-kilometre swim in open water — on August 8-9.

Marathon swimming can be moved to another location in Vaires-sur-Marne on the River Marne east of Paris if necessary.

Paris Mayor Anne Hidalgo swam in the Seine earlier this month along with Paris 2024 chief organiser Tony Estanguet to demonstrate it was clean enough for the Olympics.

The Socialist city leader plans to create three public bathing areas in the Seine for Parisians next year — a century after swimming was banned in the river.