The Belgian triathlete who withdrew from the Olympic mixed relay days after swimming in the River Seine in the individual event doesn't believe Escherichia coli (E. coli) was to blame for her illness.

The news comes as Olympic officials given the famous waterway the green light to host the marathon later this week, after another familiarisation session for athletes was cancelled due to water quality concerns yesterday. 

Claire Michel finished 38th in the women's triathlon final last Wednesday, the first event in which Olympic competitors swam for a medal in the River Seine.  

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Michel's illness resulted in the Belgian team withdrawing from the triathlon relay. 

Details of her illness were not provided by Paris 2024 organisers or the Belgium National Olympic Committee, citing the athlete's right to privacy.

"I am gradually doing better and I returned home to Belgium today," Michel wrote on Instagram on Tuesday.

"Blood tests showed that I contracted a virus (not E. coli). After three days of vomiting and diarrhoea, which left me quite empty, on Sunday I ended up needing more significant medical attention at the clinic (in the Olympic Village)."

The news emerged on the same day organisers cleared the River Seine to host a familiarisation swim for competitors in the marathon. 

A similar session planned for Tuesday had been cancelled due to concerns over water pollution.

A meeting was held on water quality early on Wednesday and attended by representatives from World Aquatics, Paris Games organisers and other stakeholders involved in carrying out the tests.