TOKYO, Nov 15 (Reuters) - A survey of the water in Tokyo bay, where the swimming leg of the triathlon will be held in the 2020 Olympics, produced mixed results, with excess levels of E.coli bacteria recorded on one day, even in areas protected by underwater screens, the organisers said on Friday.
The jump was likely caused by heavy rain, they said. As in many other major cities around the world, Tokyo processes rainwater and household wastewater via the same sewage system.
When torrential rain overwhelms the city's water treatment facilities, partly treated sewage and even raw sewage diluted with rainwater can find their way into the environment.
On one of the 12 days in early to mid-August this year, when the water screen system was installed for the test, E.coli levels were up to four times above the accepted limit, the survey showed. They were below the limit on the other 11 days.
Tokyo 2020 official Kaori Akiya said that triple-layer screens will be installed for the 2020 Games, compared with single-layer screens used during the survey, making the area, called Odaiba Marine Park, fit to host the competition.
"It could be difficult when a large typhoon comes this way, but there should be no problem in hosting events at the Odaiba Marine Park if we set up triple-layered screens and operate them properly," Akiya, the Tokyo 2020 Venue General Manager, told a news conference.
Concerns over high temperatures and water quality issues have dogged the Tokyo 2020 organisers this year.
The International Olympic Committee said last month that the marathon events will be moved to the far northern city of Sapporo to avoid Tokyo's summer heat. In August, the swimming leg of a para-triathlon race was cancelled due to high levels of E.coli bacteria found in the water of Tokyo Bay.
To help ensure spectators stay hydrated in the summer heat, organisers have decided to let them bring up to 750 millilitres of non-alcoholic drink into competition venues, a departure from the practice of recent Olympics.
"In London (Olympics) or Rio (de Janeiro Olympics), drinks from outside were prohibited for security reasons," Hidemasa Nakamura, Tokyo 2020 Games Delivery Officer, told reporters.
"But this time, heat has become such a big topic. As it is extremely important to have something to drink on hand, we've decided to let people bring in one bottle each." (Reporting by Kiyoshi Takenaka; Editing by Hugh Lawson)