David Gerrard in 2021

Inside the cool and controlled confines of the Ariake Aquatic Center, temperatures are a comfortable 27 to 28 degrees Celsius. Swimmers and divers don’t give a thought to their environs.

But in the Tokyo2020 triathlon and marathon swimming competitions, athletes are freestyle swimming in the mouth of Tokyo Bay, where water temperature and quality are close to levels deemed unsafe.

“We are literally in the lap of the weather gods,” Dr David Gerrard, one of 10 members of the International Swimming Federation’s (FINA) sports medicine committee at Tokyo2020. He is also one of perhaps a handful of people to be accredited at both the 1964 and 2020 Tokyo Olympics, as Dr. Gerrard was a swimmer on Team New Zealand here 57 years ago.

Tokyo is currently facing one of Japan’s hottest summers, which is wreaking havoc for athletes competing in the sun. And when the water in Tokyo Bay is continuously exposed to intense solar rays, the water heats up. Prior to the triathlon in the first week of Olympic play, water temperatures climbed to as high as 30.5 degrees Celsius (86.9 degrees Fahrenheit).

“If water temperature gets above 31 degrees Celsius, we are legally bound to say it exceeds the safety levels, and the event cannot proceed,” explained Dr. Gerrard. He went on to say that special paddle wheel devices floating on pontoons are helping to circulate the cooler water from the bottom of the bay to the top, and that the marathon swimming competitions, which will take place on August 4 and 5, will start at 6:30 AM, when water temperature should be at its coolest.”

Dr. Gerrard was part of a research team at the University of Otago (New Zealand) that measured  the impact of sustained high water temperatures on swimmers.

“The human body can’t sustain a core body temperature in excess of 39 or 40 degrees Celsius.” he said. “This results in hyperthermia, or heat stress, with potential life-threatening effects.  It’s also critical to replace fluids and electrolytes  which are lost through sweat.”

In marathon swimming, athletes have the opportunity to replenish fluids and electrolytes at feeding stations along the course. Coaches on the “feeding pontoons” also  observe their swimmer for any unusual behavior that might indicate the onset of hyperthermia.

If water temperature is Scylla, then water quality is Charybdis.

Apparently, Tokyo Bay stinks.

The drainage systems for rainwater and sewage are the same, which on the average day is not an issue because the sewage is treated before entering the drainage system. However, when there is a typhoon or a sustained rainfall in Tokyo, the treatment system can be overwhelmed and untreated sewage gets swept into the Bay. Years of that have resulted in polluted waters.

In order to make Tokyo Bay safe enough for competitors during the Olympics and Paralympics, measures have been taken: implementing triple-layer screens to prevent pollutants from flowing into the Bay, as well as laying of sand at the bottom of the Bay making it easier for water-cleaning organisms to thrive.

Dr. Gerrard explained that event organizers monitor the bacterial count of  E. coli and enterococci, bacterial markers of water quality. And if the water exceeds standards stipulated by the World Health Organization, the swimmers would be at risk of gastroenteritis, an infection of the digestive system, which could induce malaise, nausea and vomiting, and if not treated, dehydration.

However, he assured me that under current conditions, swimmers would have to drink a lot of Tokyo Bay to get that sick. He said that he gets daily reports of Tokyo Bay’s bacterial count, and is not concerned. “Right now, it’s a safe level. We’re very satisfied.”

Shortly after that, the rain came pouring down on Tokyo.

On the one hand, the rain is good for water temperature, he said. But on the other hand, there could also be some waste water runoff into the Bay, he added with a shrug.

Will the weather gods cooperate for marathon swimming? We will see.