Record-low Danube levels have shifted drought impacts from a mainly hydropower-driven issue toward a broader electricity-system risk across Southeast Europe. Falling river conditions have been linked to nuclear output reductions in Romania and Bulgaria. The changes also coincide with wider effects on power flows in the region.
Nuclearelectrica shutdowns tied to Cernavodă water conditions
Romania’s state-controlled Nuclearelectrica shut Cernavodă Unit 1 on July 28 due to exceptionally low Danube levels. The company began the controlled shutdown of Cernavodă Unit 2 on Aug. 13 after conditions deteriorated further. Each unit has roughly 700 MW of capacity, and together the reactors normally account for around a fifth of Romanian electricity production (Iris).
Danube flow entering Romania had fallen to around 1,350-1,400 cubic metres per second in mid-August. This compared with a multi-year August average of about 3,900 cubic metres per second. The river-level decline set the context for the nuclear curtailments at Cernavodă.
Kozloduy Unit 5 reduced as Danube levels declined
Bulgaria reduced output from Kozloduy Unit 5 by around 120 MW on Aug. 21. The plant described the move as driven by an unprecedented and critical decline in Danube levels. It was the first hydrology-related reduction of reactor output in Kozloduy’s 52-year operating history.
The nuclear-related adjustments broadened how drought affects regional power markets. Low rainfall has traditionally reduced Southeast European electricity supply mainly through lower hydropower generation, particularly across the Balkans where Albania, Montenegro, Bosnia, Serbia, Croatia and Romania all have significant hydro exposure.
River cooling constraints expand beyond hydropower
The summer of 2026 has shown a second channel for drought impacts. Large thermal and nuclear plants located along major rivers depend on sufficient water availability for cooling and associated plant processes. Under sufficiently severe drought conditions, output can fall even at plants typically regarded as firm baseload.
This makes hydrology a regional rather than purely hydroelectric risk. The effect is particularly relevant along the Danube because major electricity systems from Hungary through Serbia, Romania and Bulgaria are connected both physically and commercially.
Cross-border market effects seen during Sept. 1 trading
A reduction in Romanian nuclear generation can extend beyond Romania’s borders. It can increase Romanian imports, tighten Hungarian and Bulgarian balances, and alter power flows across Serbia and the wider Balkan market . That pattern was visible at the start of September.
Romania required roughly 1.03 GW of net imports during the Sept. 1 trading session while nuclear generation remained at zero. Romanian day-ahead electricity settled at €177.28/MWh, close to Hungary, Bulgaria and Greece, while Serbian SEEPEX jumped €34/MWh in a single session .
Drought coinciding with wind weakness raises reliance on imports and dispatchable fuels
The market impact is amplified when low river levels coincide with weak wind, high cooling demand or reduced thermal availability. In such conditions, system operators draw more heavily on imports, reservoir hydro, lignite or gas generation precisely when neighbouring systems may face similar weather constraints .
The same hydrological exposure also complicates how “firm” low-carbon generation is treated operationally. While nuclear is less weather-dependent than wind or solar on an annual basis, this summer showed that older river-cooled plants can still be exposed to extreme hydrological conditions . For Southeast Europe, drought risk increasingly needs analysis across the entire generation stack rather than only hydroelectric reservoirs.
A dry Danube can remove hydro output, constrain navigation and fuel logistics, and reduce nuclear or thermal capacity at the same time. Water availability therefore functions as an electricity-market variable with consequences spanning Romania and Bulgaria to Serbia, Hungary and the western Balkans.
