Photo/IllutrationOdaiba Kaihin Koen (Odaiba beach park) in Tokyo's Minato Ward (Asahi Shimbun file photo)

An inflow of raw sewage caused below-standard water quality in more than half of tests conducted in the summer at a swimming venue for the 2020 Tokyo Summer Olympics, organizers said.

The Tokyo metropolitan government and the Tokyo organizing committee for the Games said Oct. 4 that their survey of the seawater often found high levels of coli bacillus and other pollutants off Odaiba Kaihin Koen (Odaiba beach park) in Tokyo.

They said the high levels were caused by the many rainy days that drenched the capital in the summer.

The swimming part of the triathlon and open-water swimming events will be held off the beach for the Tokyo Olympics.

The committee said it has no plans to change the venue.

Standards for water quality have been set for both the triathlon and open-water swimming events to protect the athletes.

According to the study, the sea water quality fell below the triathlon standard on 20 of the 26 days tested, and the open-water swimming standard on 11 of 21 days.

Heavy rain caused overcapacity at sewage processing plants, and some of the untreated sewage flowed into Tokyo Bay, according to the metropolitan government and the committee.

They are considering such measures as installing triple layers of a screen that can block the flow of coli bacillus.

Odaiba has been the site of triathlon competitions and other swimming events for more than 20 years.

No sports events have ever been canceled there because of poor water quality, government officials said.