From nuclear power in Romania and Hungary to hydropower in Serbia, the region depends on the major European river to meet its energy needs.

“The Danube has given us days, not months,” Prime Minister Péter Magyar said, as plunging river levels threatened the plant that supplies around a third of Hungary’s electricity.

BUCHAREST: Romania will begin shutting down its only nuclear power plant on Thursday after the Danube’s flow fell to a record low this week and efforts to avert a complete…