On the morning of July 10, as the sun reappeared, the city reopened all three spots. Swimmers poured back in, determined to reclaim their chance. Many had traveled far for the moment. One family, led by a Chinese-born Parisian nicknamed Fan Fan, turned out in force. "I've lived here more than 20 years," she said proudly, standing by the wooden dock with her children. "It's not every day you see history change. We had to come."

Others came from much farther away. Paulo Antonialli and Rachel Schroeder, a couple from Brazil, planned a Paris holiday for Rachel's birthday, and by chance, they arrived just in time to swim in the Seine's clean waters. "There's only one Paris, and only one Seine," Paulo laughed, as they inched closer to the front of the line, without caring the length of the queue.