Europe’s 2026 Heatwave and Jellyfish Invasion Knocked 20% of French Nuclear Power Offline and Doubled Hungarian Power Prices

The jellyfish attack on Gravelines

On August 11, a massive jellyfish swarm clogged the seawater cooling pumps at France's Gravelines nuclear plant — the country's largest — forcing the shutdown of three reactors and halving output at a fourth, taking roughly 3.2 GW offline . By August 12, these combined environmental factors — drought, extreme heat, and jellyfish — had knocked about 20.4% of France's nuclear capacity offline . As of August 13, Europe's fifth heatwave of the summer was expected to remove about 15% of France's nuclear fleet capacity for the day, with six reactors fully offline, the lowest nuclear availability since August 2023 .

Hungary’s Paks plant brought to the brink

Record-low Danube water levels forced output cuts at the Paks nuclear plant, Hungary's sole nuclear station, by late July . On August 2, Prime Minister Péter Magyar warned of "critical" days ahead, saying the drying Danube could force Paks to shut down completely for the first time in over 40 years . On August 4, Hungary came close to a forced overnight shutdown of the plant; the water level stopped falling just millimeters from the cutoff point . The Paks outages removed up to 2.4 GW of capacity from the regional grid , and Hungary imposed power-use curbs to ease grid strain .

Wholesale electricity prices soared across southern and central Europe

An "unprecedented" heatwave drove summer power prices to levels normally seen only in winter peak months . French day-ahead power prices spiked 21.8% to €142.5/MWh on August 11 as the fifth heatwave tightened supply, while German prices rose in tandem as low wind speeds compounded the nuclear losses . In July, French monthly wholesale prices rose 45.8% month-on-month to €96.61/MWh, Spain rose 50.6% to €104.79/MWh, and Italy rose 18.5% to €156.77/MWh .

Hungarian day-ahead power prices nearly doubled in the week to August 3, hitting 3.5-year highs, driven by the loss of up to 2.4 GW of nuclear generation and record-low Danube levels . Italian day-ahead prices climbed to their highest level in 3.5 years on August 4 . In Slovenia, quarter-hourly day-ahead prices reached €717.75/MWh on the evening of August 7 . Prices across southern and central Europe surged to €500/MWh or more in some markets due to the compounding drought and nuclear outages .

The simultaneous power crises across Italy, Hungary, and France created a regional supply crunch, with countries forced to rely more heavily on imported fossil fuels and variable renewables, further pressuring prices upward .