A massive jellyfish swarm forced parts of the Gravelines nuclear plant offline on Aug. 11 for the second year in a row
Rising sea temperatures have made jellyfish swarms more common, disrupting nuclear plants that rely on seawater for cooling
EDF has spent heavily on preventive measures, including patrol boats, but the latest swarm still overwhelmed the system
Aug. 11 is becoming an unwelcome anniversary at one French nuclear power plant.
For the second year in a row, on Aug. 11, a massive swarm of jellyfish forced reactors offline at the Gravelines nuclear power plant in northern France. According to Politico, on Tuesday, Aug. 11, French utility provider EDF was compelled to bring parts of the facility offline after "several dozen tons" of jellyfish blocked the plant's pumping systems, the company said in a statement.
The shutdown does not pose a threat to the safety of the plant, its workers, or the environment, according to EDF.
"On-site teams are fully mobilized to ensure the safety of the facilities and to reconnect the reactors to the national power grid," the statement read.
The incident was nearly a carbon copy of a shutdown event that shuttered reactors at the same North Sea plant last year on Aug. 11, as reported by Politico. In the wake of that swarm, EDF spent hundreds of thousands of euros on preventive measures, installing cameras and deploying fishing boats to monitor the coastline.
Three fishing vessels are now "constantly patrolling off the coast of the plant" to conduct round-the-clock "preventive fishing operations," EDF said.
The boats "prevented a massive influx of jellyfish" over the weekend, but were eventually overwhelmed as the swarm ballooned from "about 100 kilograms" to "several dozen tons," according to the utility giant.
Experts say the phenomenon is tied to the warming climate. Rising sea temperatures have made jellyfish swarms increasingly common along the French coast in recent years, and those swarms can interfere with a plant's ability to draw in the seawater used to cool its reactors, which is what happened at Gravelines.
Nuclear power plants are typically built along rivers or coastlines so they can tap nearby water to cool their reactors. But the summer of 2025 saw a record number of French plants temporarily shut down as heat waves and droughts affected their water supply.
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Environmental activists seized on the shutdown, arguing that nuclear power poses problems for the marine ecosystem. "This only highlights that nuclear power plants are ill-equipped to deal with the consequences of climate change," the French branch of Greenpeace said in a statement.
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