TOKYO (AP) — A top Tokyo Olympic Games organizer pledged Tuesday to keep water clean and safe at marathon swimming and triathlon venues, where bacterial contamination was detected during the summer.

Toshiro Muto, Tokyo 2020 organizing committee CEO, said in an interview with the Associated Press in his office that officials have been trying out various measures at the Odaiba Marine Park venue, including underwater curtains to close off the venue, which have tested effectively.

Muto says water quality has improved and further measures are being tried out.

The water quality survey during the summer found E.coli at concentrations up to 21 times the levels permitted by the sport's governing body, a surprise for a country known for cleanliness. This raised concerns among athletes.

The water issue came up in early October at a project review meeting of the International Olympic Committee and the Tokyo organizing committee. Tokyo officials have ruled out moving the venue.

Muto said the metropolitan government has conducted tests on the problem using underwater screens, and Tokyo organizers are working with them to set a roadmap to improve water quality and keep it under control.

"Results of their experiments have demonstrated significant improvement," he said. "We will keep working on them so that we can take highly effective measures."

Test results have demonstrated that use of underwater screens in two layers could keep out up to 90 percent of E.coli inflow to the venue. Officials plan to test triple-layer curtains to compare results.

Muto said adding a third layer of the screens could prove even more effective in keeping the water clean at the venue.

Metropolitan officials attributed the excessive reading to Tokyo's near-record summertime rainfall that affected sewage processing capacity. Japan's capital had 21 consecutive days of rain in August, the longest streak in 30 years.

Exceeding the processing capacity of sewage facilities can cause sewage water diluted by rain to be discharged into the ocean.

E.coli counts have since decreased at least in two water quality tests, and two events at the venue were held on Oct. 9 and Oct. 15 as scheduled, according to the Japan Triathlon Union. There has been no report of health problems among the participants of the events.

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