Open water swimmers had to be due to race in the river over the weekend only for those plans to be dashed due to pollution caused by above-average rainfall in the capital.

World Aquatics decided to cancel its Open Water Swimming World Cup, which was set to act as a test event for Paris 2024, after it ruled that the water quality was below acceptable standards for safeguarding swimmers’ health.

The cancellation raises doubts over the triathlon and Para triathlon test event, scheduled to be held from August 17 to 20.

World Triathlon admitted that there were contingency plans for the event but claimed that it was "unlikely" that this would be implemented.

"For Paris 2024 and World Triathlon, the health and safety of athletes is our top priority," a statement from World Triathlon read.

"We will therefore, together with the relevant authorities, continue to carefully monitor water quality over the coming days, in the confident expectation - based on the current weather forecast - that elite athletes will compete in the Seine later this month, at the World Triathlon and Para Triathlon Test Event Paris scheduled for 17-20 August.

"In the unlikely event that water quality does not meet the requirement of World Triathlon and public health authorities, a contingency plan is in place which would see the race(s) shifted to a duathlon format.

"With a year to go before the Games, the efforts to make the Seine swimmable, led by the State and the City of Paris, continue to significantly improve the quality of the water in the Seine."

France has spent around €1.4 billion (£1.2 billion/$1.5 billion) in its attempts to clean up the Seine, with public swimming in the river made a key legacy ambition of Paris’ hosting of the Olympics and Paralympics.

When announcing the cancellation of the Open Water Swimming World Cup, World Aquatics President Husain Al-Musallam ruled that it was "clear that further work is needed" to ensure "robust contingency plans" are in place for next year’s Olympics.

Paris 2024 has insisted that "major measures have already been taken over several years" to improve the quality of the water, including the disinfection of discharges from the two wastewater treatment plants on the Seine and Marne rivers.

The French organisers also stressed that the "most significant" water quality improvement projects were due to be finished in the coming months in a bid to cope with "exceptional weather events".

Under the plans, the Austerlitz storage basin, a cylinder 50 metres in diameter and more than 30m deep, will be constructed.

The basin is expected to be able to store more than 50,000 cubic metres of water which is the equivalent of 20 Olympic-sized swimming pools.

"This reservoir will allow event organisers to be better prepared for exceptional weather events by preventing wastewater from being discharged into the Seine in the event of heavy rain," a statement from Paris 2024 said.

"Thanks to this basin, the excess water will flow into the sewer system for treatment."

The VL 8, a 10km long high-capacity collector between Essonne and Val-de-Marne is also set to be in operation along with another rainwater treatment plant.

Paris 2024 said that the Val-de-Marne basin would be designed to receive rainwater and treat it before it is discharged.