Newly obtained documents have revealed the extraordinary nature of a fish event that disrupted operations at Canada’s largest nuclear power plant nearly two years ago. The incident, which involved an overwhelming number of gizzard shad fish clogging cooling systems at the Bruce Nuclear Generating Station in February 2025, posed a significant challenge to the plant’s safety protocols.
The revelations from over 1,200 pages of federal and provincial records shed light on how the unexpected influx of gizzard shad, a cold-sensitive species seeking refuge in the plant’s warm water discharge during winter, caught the operators off guard. Both Bruce Power and Canada’s nuclear regulator characterized the event as unprecedented and a test to the plant’s defenses against such ecological anomalies.
While Bruce Power acknowledged the “novel environmental event” and the disruption caused by the fish runs in early February, experts like David Novog emphasized the importance of maintaining multiple layers of defense at nuclear plants to ensure reactor safety. Despite the challenges posed by the fish event, former principal scientist Douglas Boreham reassured that the reactors responded as designed, emphasizing that there was no compromise to safety.
The Canadian Nuclear Safety Commission (CNSC) highlighted the potential consequences of the fish die-off on the plant’s cooling systems, which led to the shutdown of Unit 2 and reduced power at Unit 1. The massive number of gizzard shad in the vicinity of the plant on a single day in February 2025, estimated at 8.1 million, far exceeded previous public counts and raised concerns about the impact on the plant’s operations.
The incident also had implications for Ontario’s electricity grid, with the shutdown of a reactor causing a strain on the province’s power supply. The disruption at Bruce Power reflects a broader trend of environmental factors affecting nuclear plants globally, as seen in cases like the Cernavoda Nuclear Power Plant in Romania and the Gravelines nuclear plant in France.
Following the event, Bruce Power undertook mitigation efforts, investing nearly $10 million in measures to prevent future disruptions from fish events. These include physical barriers, acoustic deterrents, monitoring technologies, and an AI system to detect and deter large fish gatherings near the plant’s cooling intakes. As the reliance on nuclear power for low-carbon electricity grows, the focus on preventative measures to avoid such incidents will be crucial for the industry’s resilience against changing environmental conditions.