Tokyo 2020 and the Metropolitan Government conducted a water quality assessment in Tokyo Bay, the location of the marathon swimming and swimming leg of the triathlon, to mirror the 21 days of competition at the Olympics and the five days of action at the Paralympic Games

It revealed the quality of the water only matched FINA standards on 10 days and adhered to ITU regulations on six days.

The results showed levels of E. Coli up to 20 times above the accepted limit and faecal coliform bacteria seven times higher than the permitted levels.

International Olympic Committee (IOC) Coordination Commission chairman John Coates, speaking following the conclusion of the two-day Project Review visit to the Japanese capital, admitted the readings resulting from the survey were "were not what they should be".

"FINA took note today of the Tokyo 2020 announcement of the water quality test results in Odaiba," FINA said in a statement.

"As the world governing body for Aquatic sports, FINA will keep working closely with the Tokyo Metropolitan government and Tokyo 2020 Organising Committee to ensure the best available venue and environment for the marathon swimming events in 2020."

Tokyo 2020 have vowed to implement water quality improvement measures in the lead-up to the Games to ensure that the venue "satisfies all relevant International Federation standards".

These include the installation of underwater screens, which "tests have shown to be particularly effective in improving water quality", according to Tokyo 2020.

In a statement in response to the results, Tokyo 2020 have also promised to "consider all necessary measures to ensure the smooth operation of events at Odaiba Marine Park, including amendments to event dates and/or times in response to weather conditions".

Organisers claim the reason the standards were not met was due to significant rainfall in the month of August.

"In August 2017, there was rainfall in the Tokyo area on 21 consecutive days, the second highest number of consecutive days of rain recorded in August since 1977," the statement added.

Tokyo 2020 have also defended the quality of the water at the Odaiba Marine Park, highlighting major events in marathon swimming and triathlon have been held there in the past.

The venue has hosted Japan’s National Triathlon Championships for more than 20 years, while Japan Swimming Federation staged its Tokyo Marathon Swimming events there between 2009 and 2013.

The Japan Open Water Swimming Championships have taken place at the venue since last year, Tokyo 2020 added.

"The Tokyo Metropolitan Government and Tokyo 2020 will continue to make the best possible preparations to ensure that the venue satisfies all relevant International Federation standards, and that all athletes can perform at their best," Tokyo 2020 said.

Water quality issues also dominated the build-up to last year's Olympic Games in Rio de Janeiro, with concerns raised over pollution levels at Guanabara Bay, which played host to sailing events.