I was in Paris a few months ago. The Seine is one nasty looking river. I can’t imagine swimming in that.
To people who say “Oh, this is no big deal” I would scoop a glass of water from a random spot in the Seine, hand it to them, and say “Okay. Put your mouth where your money is. Drink this glass of Seine water.”
And it HAS to be a clear glass.
And the person drinking must watch the water be scooped out.
And no plugging of the nose while drinking.
Wait until they have the Olympics in India & have to swim in the Ganges!