Paris is staging its first high-diving competition in the Seine, with athletes launching themselves from a 20-meter platform in front of the Eiffel Tower — a spectacular new test of the city’s effort to reclaim its river for sport. High diving concludes Saturday with the final two rounds and medal events, while the broader European Aquatics Championships run through Aug. 16. “There are things that are within our control, and there are uncertainties that are inevitably linked to any outdoor activity,” said Maxime Sauvage, Paris deputy mayor in charge of sports, sports facilities and equal access to sport.