Belgium has withdrawn its swimmers from the mixed relay triathlon race on Monday and Switzerland has changed its roster of swimmers to accommodate those who got sick. Athletes from both countries fell ill after competing in the initial triathlon races last week.

Belgian triathlete Claire Michel got sick after swimming in the competition in the River Seine Wednesday, and was reported days after she swam, its National Olympic Committee said in a statement.

It did not specify Michel’s illness, which was reported days after she swam in the River Seine during the women’s triathlon on Wednesday, where she finished in 38th place.

“The BOIC and Belgian Triathlon must unfortunately announce that the ‘Belgian Hammers’ will not be starting the mixed relay at the Paris Olympic Games tomorrow. The decision, like this communication, was taken in consultation with the athletes and their entourage,” the statement read.

The Swiss team replaced Adrien Briffod, who withdrew because of a gastrointestinal infection. Simon Westermann will replace him.

It is unclear if Briffod’s infection is related to the Seine’s water quality.

“A survey of my colleagues from other countries has so far not revealed any accumulation of gastrointestinal illnesses among the athletes who started the individual race last Wednesday,” Betschart said.

Countries called on Olympic organizers to learn lessons from this year’s uncertainty surrounding the cleanliness of the water in the River Seine, which caused uncertainty as to guaranteed training and the safety of the water itself.

Despite the illnesses, World Triathlon and Paris 2024 have said the mixed triathlon will proceed Monday and claimed that the river’s water quality had improved.