MUNICH — The mesmerizing scene along the banks of Munich’s lime-green Isar River on a recent summer afternoon made me, an out-of-towner, quiver with envy. Clusters of students, off-duty office workers, families and nude sunbathers were sprawled out on blankets with bottled beer and light meals. Every so often, a swimmer or tuber passed by, carried by the swift current.

In 2000, before the climate crisis accelerated, turning summers into slogs punctuated by a slew of heat records, the city of Munich undertook a sweeping restoration of the Isar, which flows north from the Alps through downtown and into the Danube. The 11-year, $38 million endeavor involved purifying the Isar’s waters, expanding its floodplains and modifying its banks to accommodate the torrential spring snowmelt.