The Danube river is running so low that nuclear power plants in both Hungary and Romania have had to shut down, cutting electricity to millions of people.

Romania shut down both of its nuclear reactors on July 29, 2026, after the Danube dropped too low to cool them, according to Reuters. In Hungary, operators took one reactor offline at the Paks nuclear plant, and on July 30 Prime Minister Peter Magyar warned that the whole plant might have to shut down by Thursday or Friday, Reuters reported. Paks supplies nearly half of Hungary's electricity from its four reactors, per Euronews.

The water shortage is extreme. Romania's National Institute of Hydrology measured the Danube's flow where it enters Romania at just 1,600 cubic metres per second on a recent Wednesday. The July average is 4,700. The institute expected the flow to drop further to 1,500 by the following Tuesday, according to BBC. The Danube is Europe's second-longest river, stretching 2,857 km through 19 countries from Germany to the Black Sea.

Nuclear power plants need a lot of water to stay safe. They use river water to cool down steam after it has spun the turbines that make electricity. Think of it like a car radiator: without enough water flowing through, the engine overheats. When river levels fall below a safe minimum, plant operators must shut the reactors down to avoid danger. Hungary's 9th National Report under the Convention on Nuclear Safety says the Danube can serve as a backup cooling source for Paks in a severe accident, but that plan assumes the river has enough water. The plant's low-level solid waste disposal site sits about 20 km west of the Danube and 60 km south of the facility.

The effects go beyond power. Receding water in Croatia exposed the remains of a sunken Hungarian cargo ship. In Serbia, low levels revealed the hulks of a German river flotilla. A resident of Ruse, Bulgaria, found bones on the riverbed that experts identified as mammoth remains, including a lower jaw, two tusks, and possibly a rib, per BBC. River tourism has also been hit, with cruise boats and riverside businesses disrupted by channels too shallow to navigate.

This is all happening during a wider European heatwave. Wildfires were burning in France and Spain in late July 2026, and French wildfires affected 40,000 businesses, according to Euronews. The combination of drought, fires, and industrial disruption is straining power cooling, farm water supplies, and shipping routes across the continent.

The two affected plants, Paks and Romania's Cernavoda, normally provide a steady stream of power that the region relies on around the clock. Both shutting down at once takes a large amount of clean electricity off the grid right when summer demand is highest.

Why this matters for the wider region is straightforward. If the Danube keeps dropping, a full Paks shutdown would leave Hungary needing to buy power from other countries, at a time when its neighbors' grids are already strained by the heat. Romania has already lost its only nuclear power source with the Cernavoda shutdown.

A big unknown is how long this lasts. Forecasts from Romania's hydrology institute suggest the river has not yet hit its lowest point. There is no sign in the data of when flows might recover enough for the plants to restart. Even once river levels rise, nuclear plants need regulatory approval before they can switch back on, which can delay the return of power.

The Danube is Europe's second-longest river and a lifeline for six nuclear reactors across two countries. The fact that the same drought has exposed sunken ships, mammoth bones, and the fragility of the region's power supply shows just how central this river is, and how much depends on it having enough water.