In the early hours of 4 August 2026, Hungary's largest nuclear power plant came within millimetres of shutting down completely. The reason was not a mechanical failure or a safety alert. The Danube — the river that keeps the plant's reactors cool — had dropped to a record-low level. Nuclear power plants use large amounts of water to absorb the heat they generate. Without enough water flowing past the plant, the reactors cannot be cooled, and they must be shut down to prevent overheating. Hungarian prime minister Péter Magyar said that around 1:30 a.m. the water level stopped falling and by morning had risen 1.5 cm, allowing the last running turbine to keep going. The plant, called Paks, is now running at just over 10% of its normal output. The Guardian

The problem has been building since late July. Nuclear plants along the Danube in both Hungary and Romania had to cut production as river levels fell. On 31 July, Magyar warned that low Danube levels could keep Paks shut for weeks. By 2 August, he called the coming days "critical" and confirmed the plant would not generate power the next day, as temperatures approached 40°C. In a Facebook video on 3 August, Magyar said the hardest five days were ahead and that experts had previously warned the Danube's falling level created a critical need for a new, modern safety system. Reuters

The water dependency is real and direct. In a Facebook post on 1 August, Magyar noted that the Danube measured 97 cm in 2018 and stands at 121 cm now, in the context of the cooling-water requirements for Paks II's two new reactors. He also reported Danube readings of 390 cm at Passau and 218 cm at Bratislava in a 30 July post, and questioned whether the Austrian and Slovak prime ministers should be asked not to shut off the Danube's water. The Danube flows through ten countries before reaching Hungary. The much higher readings upstream at Passau and Bratislava show how the river loses water as it passes through each country on its way to Paks.

Hungarian energy minister István Kapitány said on 4 August that energy-saving measures lowered consumption enough to keep the power grid stable. These measures went well beyond the electricity sector. The grocery chain Lidl in Hungary changed its baking shifts and turned off its drink fridges during peak hours. Electric car chargers in its car parks could only be used until 5 p.m., even as temperatures neared 40°C. The Guardian

Romania faces a parallel crisis at its Cernavodă nuclear plant and has taken more dramatic steps. The Romanian government declared a state of emergency as record-low Danube water levels cut power output and threatened nuclear operations in both countries. On 3 August, Reuters reported that Romania carried out a controlled explosion of a rock outcrop on the Danube to redirect cooling water to its nuclear plants. The government then celebrated a two-centimetre rise in the water level following the blast. The manager of the Cernavodă plant said the rise should keep the facility running for a few more days, with more interventions planned, including sinking old barges to further divert the river's flow. Reuters

The broader context here is the collision of two dependencies. Nuclear power needs river water for cooling, and the Danube is a shared resource flowing through ten countries before it reaches Hungary and Romania. When the water drops below the level the cooling systems need, the physics is unforgiving. Reactors must reduce output or shut down. There is no workaround once the river itself becomes the constraint. Romania's controlled explosion and its plan to sink barges are improvised fixes to a water crisis, not long-term solutions.

The stakes at Paks are especially high. The plant supplies roughly half of Hungary's electricity. Running it at 10% capacity during a heatwave — when people need power for air conditioning the most — puts pressure on both power generation and distribution. The energy-saving measures, from Lidl's changed shifts to EV charger curfews, show how deep the demand-side response had to be to keep the system intact.

Magyar's references to Paks II, a planned expansion with two additional reactors, add a forward-looking question. If the current cooling system cannot sustain the reactors that already exist during a drought measured in centimetres of river depth, the decision to add two more reactors — each with its own cooling needs — invites scrutiny that Hungarian officials will need to address. The comparison Magyar drew between the 97 cm level in 2018 and the current 121 cm, framed around Paks II's needs, suggests this question is already part of the political conversation in Budapest.

Romania's state of emergency, its controlled explosion, and the planned barge-sinking show that Bucharest is treating the Danube's low water as an active crisis that requires physically changing the riverbed. The Cernavodă plant manager's assessment that the two-centimetre rise buys only a few days suggests these measures are temporary, not a lasting fix. Further interventions are expected.

Both governments are managing a water emergency that no single country can solve. The Danube's flow at Paks and Cernavodă depends on what happens upstream in Germany, Austria, and Slovakia. Magyar's public questioning of whether Vienna and Bratislava should be asked not to shut off the Danube's water, however unusual the framing, identifies the core tension. Each country along the river draws from the same shrinking resource, and each has its own energy and water priorities. The coming days will test whether the reprieve at Paks holds and whether Romania's interventions at Cernavodă buy enough time for river levels to recover, or whether further cuts become necessary.