If you're visiting Paris this summer, you may want to add swimming in the Seine to your itinerary. And after the heat this city has seen in the past few weeks, you may absolutely need to.

For a century, swimming in the dirty Seine was unthinkable. Now, a $1.6-billion engineering marvel has turned the French capital’s river into its ultimate summer escape.

Paris has opened three supervised swimming sites in the Seine for the second summer in a row