If the triathlons do not go ahead on Wednesday, Friday remains a back-up date for both events.
If the water quality is still not good enough by Friday, organisers have said the event could be contested as a duathlon - just the cycling and running legs - as a last resort.
The triathlon made its Olympic debut in Sydney in 2000. The event features 1500m of swimming, a 40km bike ride and a 10km run to finish.
While a mixed relay was added in Tokyo three years ago, there has never been a duathlon in the Olympics. Ordinarily that would consist of a 40km cycle and a 10km run.
However, at the Paris Test Event in 2023, a duathlon format was trialled, with the swim replaced by an additional 5km run.