Uncertainty is continuing to surround the ability of the River Seine to host the Opening Ceremony, Triathlon and Marathon Swimming at the 2024 Olympic Games.

The French government have spent a staggering $1.4 billion in an effort to clean the river up, which has been banned for swimming in for over 100 years due to bacteria and unsafe water hygeine.

Despite that, the river will host the Opening Ceremony in an Olympics first, with athletes to float up the river on boats rather than march into the stadium, before it also hosts the swimming portion of the Triathlons, and the Marathon Swimming - 10-kilometre open water events - at the 2024 Games.

Just three weeks out from the Opening Ceremony however, a rehearsal for the event had to be postponed this week over dangerously unsafe levels of faecal bacteria in the water.

That has thrown doubt over the river's ability to be ready to go for the July 27 (AEST) opening ceremony, or the events which follow it.

According to Euro News, tests conducted in the river between June 18 and 20 found concentrations of E.coli bacterica ten times higher than the maximum threshold set by sports organisers to hold open water events.

While a test event in the Triathlon was held last year in the Seine, World Aquatics cancelled the hosting of the Open Water Swimming World Cup there with the Seine not at acceptable levels to hold sport.

Further doubts have been thrown over the venue given French president Emmanuel Macron cancelled his swim in the river on June 23 which was supposed to put its safety beyond all reasonable doubt.

It likely didn't help that the French general population, angered over the money spent on the river, the impacts of the Olympics on the city, and a snap election called just weeks out from the Games, started a social media campaign to "#JeChieDansLaSeineLe23Juin", or, in English, "I poop in the Seine on 23 June".

It's unclear exactly how much damage that did to the bacterical matter in the Seine, but it's clear that with the cancellation of this week's dress rehearsal, there are major issues.

On their part, Parisian authorities are suggesting "unfavourable hydrological conditions" are hampering clean up efforts, with "rainfall, high flow, little sunshine and temperatures below seasonal norms" hampering efforts to clean the river up.

While Games organisers cross their fingers and pray for the best, World Triathlon - speaking to tri247.com - have expressed "great confidence" that the events of the Games will be able to go ahead as scheduled.

“We have great confidence in the work of the City of Paris authorities to ensure the water quality will meet the necessary standard for Triathlon and Marathon Swimming competitions during the Games. We are still more than one month away and the conditions are improving, even though some of the latest results are impacted by the meteo conditions in Paris in the last weeks (heavy rains)," the body said.

“Generally, water quality in the Seine continues to improve every day. By the time of the Games, bacteriological pollution in the Seine will have been reduced by 75% thanks to the range of actions undertaken by our partners."

It's unclear what the back up plans are for the Opening Ceremony, Marathon Swimming or Triathlon if it came to that.