Water quality tests at Odaiba Marine Park in July and August showed that with the exception of one day in a 12-day test event period, the use of underwater screens reduced the quantity of coliforms inside screened areas to within the stipulated guidelines set out by International Federations.

The Park is due to stage the Tokyo 2020 marathon swimming and triathlon events next year and the surveys found that the levels of enterococci bacteria was within the agreed limits.

Additional tests were sought when the swimming section of the triathlon test event for next year's Paralympic Games in Tokyo was cancelled in August because of high levels of E.coli bacteria found in the water.

Owing to rainfall, levels outside the screened areas exceeded the targeted levels on four days.

To further improve conditions during Games time, Tokyo 2020 plans to deploy triple-layer underwater screens.

Using the same testing period, Tokyo 2020 found that the recommended maximum water temperature of 31 celsius was not exceeded in any test zone.

The maximum temperature recorded was 30.8 celsius as temperatures inside screened areas were recorded at an average of 0.8 celsius higher than those recorded outside.

As well as installing triple screens, underwater screens will be used to prevent water temperature rises.

In collaborating with Tokyo Metropolitan Government, Tokyo 2020 will also continue to analyse the causes of poor water quality and odours and review methods for ensuring appropriate water quality and temperature with experts.

The start time of the events at Odaiba Marine Park are also being considered for an earlier start time and a final decision will be taken at the International Olympic Committee's Executive Board meeting due to take place in Lausanne between December 3 and 5.