When I say Le mardi et le jeudi , [je nage] or [ je faire de la natation] à cinq heur. Which one would be correct?

Hi Fran,

You would use ‘faire de la natation’ as it represents the activity ‘to go swimming’ rather than the physicality of doing swimming movements.

So you might say -

‘Je me suis fait mal en nageant’ = ‘I hurt myself while swimming’

But

‘Faire de la natation est bon pour la santé‘ = ‘Swimming is good for your health‘

Tricky and very subtle I know but hope this helps!