Photo/Illutration An athlete competing in the women’s marathon swimming event for the Tokyo Olympics at Odaiba Marine Park in the capital’s Odaiba district on Aug. 4 (Takuya Isayama)

After attracting international attention over athletes complaining that Tokyo Bay smelled like “a toilet,” it turned out to be the scorching heat, not a foul stench, that troubled Olympic swimmers competing there on Aug. 4.

“The water doesn’t smell bad compared to two years ago,” said Yumi Kida, who finished 13th in the women’s marathon swimming race. “The water quality has also been improved.”

The water quality of the bay off Odaiba Marine Park in Tokyo’s Odaiba district became a major issue after athletes, who competed in pre-Olympic testing events held in the area in August 2019, complained about a foul odor in the water.

Triathlon races for pre-Paralympic testing events were scheduled to be held six days later, but the swimming was canceled after fecal coliform levels exceeded a baseline established by the International Swimming Federation.

Fecal coliform bacteria and the foul odor in the water are caused by central Tokyo’s sewage system, according to officials.

Lavatory water, industrial wastewater, and rainwater became mixed in the sewage system. When heavy rains hit, the sewage gets discharged into rivers and the sea without being sufficiently processed.

The Tokyo metropolitan government responded by building a facility to retain the unprocessed sewage without releasing it into the environment, even in the event of a downpour.

Officials also poured sand from Kozushima island, part of the Izu island chain south of Tokyo, into the waters off Odaiba to help the living organisms there thrive and consume organic matter to clean up the sea.

But the trump card in the fight against the bad smell was the triple-layered polyester screens, covering up to 5 meters below the sea level, that Olympic organizers set up underwater to stop fecal coliform bacteria from flowing into the competition area.

On Aug. 4, 25 athletes swam 10 kilometers for about two hours in the race.

“The water was dirty, but didn’t smell bad,” said a man in his 40s who worked as a volunteer at the venue. “I think (the measures) were a success.”

Kida, 36, said what she struggled with during the competition was not the funky odor but the heat.

“The race was tough because the water temperature was high,” said Sharon van Rouwendaal of the Netherlands, who won silver at the women’s marathon swimming event.

Central Tokyo recorded an overnight low of 25 degrees or higher from Aug. 3 through Aug. 4, according to the Japan Meteorological Agency.

The water temperature in Odaiba had already reached 29 degrees before the marathon swimming race started at 6:30 a.m. on Aug. 4. The International Swimming Federation sets the upper limit for water temperature at 31 degrees.

Olympic organizers used a device to circulate the water to lower the overall water temperature.

“I saw even top athletes from overseas slow down in the competition,” said Kida. “To win a race, we have to not only swim fast but also adapt to the environment.”

(This article was written by Chiaki Ogihara, Yusuke Saito and Hidemasa Yoshizawa.)

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