Danube low water in 2026, why Romania and Hungary had to shut down their nuclear plants

The short answer

Romania has shut down Cernavoda, its only nuclear power station, completely. It normally supplies around 20 percent of Romanian electricity demand and draws all of its cooling water from the Danube. The first unit went offline at the end of July, the second followed in mid August.

In Hungary, the Paks nuclear plant and its four units were taken down. It was the first complete shutdown in 44 years of operation. The site covers a substantial share of Hungarian generation, and around 2,000 megawatts fell away.

The decisive point is usually shortened in the reporting. What is missing is not primarily the water. It is that the intake openings of the cooling pumps sit too high. The Bulgarian plant at Kozloduy runs without restriction despite even lower levels, because its pumping station was designed differently.

What happened in recent weeks

The summer of 2026 has left central European rivers with less water than at any point in decades. According to an analysis by the European climate service Copernicus published at the start of August, almost two thirds of the Danube recorded the lowest flow volumes in 34 years during July.

On 27 July the Romanian operator Nuclearelectrica reported the controlled shutdown of unit one at Cernavoda in a mandatory disclosure. Three days later, on 30 July, the Hungarian operator MVM announced that low water would force all four units at Paks out of service within 24 to 72 hours.

By 1 August a complete stop was being prepared at Paks, after output across all four units had been reduced step by step. On 2 August it stood at only twelve percent. Prime Minister Peter Magyar announced that the last reactor unit would be taken down overnight into Sunday.

In Romania the navy tried in the meantime to work against the problem by technical means. Around fifty kilometres upstream, at a fork of two Danube arms near the village of Izvoarele, a rock was blasted so that more water would flow into the arm that supplies Cernavoda. Gravel from four barges was sunk at another point to steer the inflow. The level at Cernavoda rose slightly afterwards, which extended operation of the second reactor by a few days. It was not enough for a longer supply.

In mid August the Romanian energy ministry announced that the second reactor would also be taken down. The complete shutdown was to be finished in the course of one morning.

Why a power station needs water

A short look at the technology is worth it, because it explains almost everything about this event.

There are two designs. With once through cooling, river water is taken in, led through the condenser and returned warmed. With circuit cooling through cooling towers, part of the water evaporates and the need for fresh water is considerably smaller.

For plants on a river, two quantities therefore matter, and they are often confused. The first is the volume of water, that is whether enough water flows past at all. The second is the water temperature, because water that is too warm cools less well and, for reasons of water protection, often may not be returned warmed any further.

In the present case a third quantity comes in, one that rarely appears in textbooks and that decided the matter here.

The real reason lies in the installation height

According to the operator and an analysis by the association Nuklearia, the volume of water in the Danube is still sufficient on paper. The problem lies elsewhere.

At the Paks site the suction pipes of the cooling pumps now sit above the water level. The Danube level there was 28 centimetres below the previous record low from 2018.

According to that analysis, lowering the intake would be technically possible and would allow continued operation even at the current water level. That is a construction job, however, not something that can be done within a few days.

The comparison that explains the story

The most revealing thing about this summer is a power station that was not shut down.

The Bulgarian nuclear plant at Kozloduy is also cooled with Danube water and continued to run without restriction. In terms of water level the situation there was in fact more extreme. At the end of July the Danube at Kozloduy was 2.03 metres below normal low water, while at Paks it was 1.25 metres at the same time.

The difference lies purely in the design. The cooling water pumping station at Kozloduy was built for a hundred year low water event.

The lowest Danube level ever measured at that site is still above the design value of the pumping station. That is exactly why Kozloduy keeps producing.

This turns a climate story into an engineering story as well. The same drought, the same river, three power stations, three completely different outcomes. The difference was decided decades ago on a drawing board.

How much electricity is actually missing

The scale is considerable, and it hits two countries differently.

To put the Hungarian case in context, a capacity of 2,000 megawatts is roughly what two large conventional power station units deliver. The loss also came in the middle of a heatwave, which is precisely when air conditioning drives consumption up.

Both countries have therefore called on their populations to save. In Hungary the request is to use no additional electricity between 5 pm and 10 pm, meaning neither charging electric cars nor running extra air conditioning during that period. The government also called for water to be saved.

The emergency measures

What has been attempted in technical terms over recent weeks is unusual and shows how serious the situation is.

In Romania the navy blasted a rock in the riverbed to direct the flow of water into the supplying Danube arm. In addition, gravel from four barges was sunk at another point to steer the inflow. The effect was measurable but small. Defence minister Radu Miruta said operation of the second reactor had been extended by a few days as a result.

In Hungary the government ordered the construction of an underwater barrier wall to steer the current near the power station. Two 80 metre push barges are also to be stationed at Paks.

Both measures are improvisation under time pressure. They show that the actual solution, namely a structural adjustment of the intake points, is not possible at short notice during operation.

The economic consequences

The loss does not stop at the electricity bill.

In Romania the authorities warned that in the worst case large industrial companies would have to limit their consumption during the evening hours. At the start of August the government announced that the vehicle manufacturers Dacia and Ford would suspend production in the country until 19 August in order to reduce the electricity deficit.

This is the point at which an energy topic becomes an economic one. Suspended vehicle production affects suppliers in several countries, logistics, plant agreements and the trade balance.

There is a second, less visible level. A country that suddenly loses twenty percent of its generation has to import electricity or run more expensive power stations. Both feed through into wholesale prices, and those prices move into end customer tariffs with a delay.

Inland shipping suffers from the same water levels. Less cargo per vessel means higher freight costs per tonne, which makes raw materials and intermediate goods more expensive for industrial operations along the river.

What a country does when a fifth of its generation disappears

The loss of a baseload power station cannot simply be replaced by more wind or more sun, and the reason is a matter of timing.

In practice three routes remain, and all three are expensive.

The first is imports. Both countries are connected to the European grid and can draw electricity from neighbouring countries. That works technically, but it costs money and depends on the neighbours having enough themselves. In a region wide heatwave that is precisely not a given.

The second is the use of more expensive domestic power stations, as a rule gas or coal. They stand ready as a reserve but produce at higher cost per kilowatt hour. In a market where the most expensive plant needed sets the price for everyone, that lifts the wholesale price for the whole region.

The third is reducing demand. That is what is happening at the moment, first through appeals to the population and at the next stage through agreements with large consumers. The announced production suspension at two vehicle manufacturers already belongs in this category.

The timing is notable. Electricity scarcity was long regarded in central Europe as a winter subject, because that is when heating and lighting are needed. The risk is now shifting into high summer, when cooling drives consumption and rivers carry less water at the same time. Both effects reinforce each other.

Why nuclear plants in particular are affected

It would be wrong to turn this into a special case of nuclear energy. Every thermal power station on a river is affected. There are nonetheless reasons why nuclear plants appear more often in the headlines in summers like this.

For one thing they are large. A single unit delivers capacity on a scale that is immediately noticeable in the grid. If a small gas plant fails, hardly anyone notices.

For another they have a comparatively low thermal efficiency. Put simply, they give off more waste heat to their surroundings per kilowatt hour generated than modern gas plants do, and therefore need more cooling.

And finally they are designed for continuous operation. A nuclear power station cannot be ramped up and down arbitrarily often and arbitrarily fast. Every load change stresses material and is regulated by permit. When a plant is throttled, it happens step by step over hours to days. That is exactly what could be observed at Paks, where output was first reduced and then run down completely.

The same applies in reverse for the return. A power station that has gone offline is not available again within hours, even if the level rises.

Not a regional problem

The Danube is not the only river with historically low levels.

On the Rhine the gauge at Kaub showed 29 centimetres at the end of July. In Germany around 44 percent of the measuring points on the Rhine most recently reported extremely low water, on the Elbe it was 16 percent and on the Danube around 78 percent. The Federal Institute of Hydrology reported that rain showers lift water levels only briefly and that the falling tendency prevails overall.

Electricity production had to react elsewhere too. The Swiss nuclear plant at Beznau throttled its output because of high water temperatures in the Aare, so for the opposite reason. Not too little water, but water that is too warm.

The research network World Weather Attribution classifies the current drought as intensified by human caused climate change and expects the situation to worsen further.

Why this is a planning subject and not a weather subject

From the comparison of the three sites a conclusion can be drawn that reaches beyond this summer.

Power stations are built for decades. Paks began operating 44 years ago, and Kozloduy and Cernavoda also date from a time when today's water levels were regarded as very unlikely. The design followed the measurement series available then.

That is precisely where the problem lies. Design values rest on observations of the past. If the climate shifts, the frequency of extreme values shifts with it, and an event that should statistically occur once in a hundred years can occur considerably more often.

For operators that means an uncomfortable choice. Either you retrofit, which costs money and requires downtime, or you accept that the plant will not be available in certain summers. For grid operators it means that firm capacity in summer has to be calculated differently than before.

The same question arises for conventional power stations on rivers, for cooling water in the chemical and steel industries, and for inland shipping.

Frequently asked questions

Why was Cernavoda shut down

Because the water level of the Danube has fallen so far that cooling could no longer be assured. The plant draws all of its cooling water from a Danube arm and normally supplies around 20 percent of Romanian electricity demand.

Why did Paks have to go offline completely

Because the intake pipes of the cooling pumps sit above the current water level. The volume of water in the Danube would be sufficient on paper, but it can no longer be taken in for structural reasons. It was the first complete shutdown in 44 years of operation, and around 2,000 megawatts fell away.

Why does the Bulgarian plant keep running

Because the cooling water pumping station at Kozloduy was designed for a hundred year low water event. The lowest level ever measured there is still above the design value, even though the low water at 2.03 metres below normal was more pronounced than at Paks with 1.25 metres.

What are the economic consequences

In Romania, Dacia and Ford are suspending production until 19 August in order to reduce the electricity deficit. Authorities did not rule out restrictions for large consumers during the evening hours. In Hungary the population is asked to use no additional electricity between 5 pm and 10 pm.

Is this an isolated case

No. Almost two thirds of the Danube recorded the lowest flow volumes in 34 years during July. On the Rhine the gauge at Kaub showed 29 centimetres, and around 44 percent of Rhine measuring points reported extremely low water. In Switzerland a nuclear plant throttled output because of water temperatures that were too high.

Assessment

What occupies me about this story is less the drought than the comparison of the three sites. The same river, the same summer, and one power station keeps running while two stand still. The difference was not decided this year but decades ago, in the question of how deep to set a pumping station.

That shifts the debate to a place where it is rarely held. Nuclear power is usually argued over along the lines of safety, cost and waste. Availability in summer barely features, although this year it decided a substantial part of the electricity supply in two countries.

I also find it remarkable how quickly a technical detail becomes an economic event. Between the height of an intake pipe and a suspended vehicle production there are only a few steps, and none of them has anything to do with energy policy in the narrower sense.

What seems most important to me for further observation is not the water level of the coming weeks but the question of which operators now retrofit. The analysis of Paks suggests that lowering the intake would be technically feasible. Whether it comes decides whether this summer remains an exception or is the first of many.

Figures check

All statements were checked against publicly accessible sources on 15 August 2026.

Complete shutdown of Cernavoda, share of around 20 percent of Romanian electricity supply, complete cooling water withdrawal from a Danube arm, blasting of a rock near Izvoarele around fifty kilometres upstream, sinking of gravel from four barges and the statement by defence minister Radu Miruta on extending operation by a few days, from a report by ZDF of 13 August 2026.

Complete shutdown of Paks, first complete shutdown after 44 years of operation, statement by prime minister Peter Magyar on taking down the last unit, the call to save electricity between 5 pm and 10 pm, and the figures on measuring points with extremely low water of around 44 percent on the Rhine, 16 percent on the Elbe and around 78 percent on the Danube, from a report by ZDF of 2 August 2026, which draws among other things on the Federal Institute of Hydrology.

Partial shutdown at both sites because of record low water, the state of preparation for the complete stop at Paks as of 1 August, output of twelve percent as of 2 August, low water of 2.03 metres below normal at Kozloduy compared with 1.25 metres at Paks, design of the pumping station at Kozloduy for a hundred year low water event, and the assessment of a possible lowering of the intake, from a specialist article of August 2026 reproducing an analysis by the association Nuklearia.

Announcement by the operator MVM of 30 July 2026 on the shutdown expected within 24 to 72 hours, loss of around 2,000 megawatts, Danube level at Paks 28 centimetres below the 2018 record, gauge at Kaub on the Rhine at 29 centimetres, and the reference to the mandatory disclosure by Nuclearelectrica of 27 July 2026 on the controlled shutdown of unit one and to the output reduction at the Beznau nuclear plant because of high water temperatures, from a specialist article of 31 July 2026.

Lowest flow volumes in 34 years across almost two thirds of the Danube according to an analysis by Copernicus published on 10 August 2026, production suspension by Dacia and Ford until 19 August, possible restrictions for large consumers during the evening hours, the order for an underwater barrier wall and the stationing of two 80 metre push barges at Paks, from a report by Euronews of 14 August 2026. Classification of the drought as intensified by climate change according to a report by the research network World Weather Attribution, cited in the same source.

This article is for information. It contains no investment advice, no recommendation to buy or sell, and no assessment of individual securities.