Almost two years after an unusual incident with fish at Canada’s largest nuclear power plant raised concerns about reactor safety, newly obtained documents shed light on the extraordinary nature of the event. Experts are cautioning that atypical ecological circumstances are posing a growing challenge for nuclear facilities globally.
In February 2025, a massive influx of gizzard shad overwhelmed the cooling systems at the Bruce Nuclear Generating Station near Tiverton, Ont., resulting in the shutdown of one reactor, reduced power at another, and dead fish littering the shores of Lake Huron for several days. Obtained federal and provincial records, totaling over 1,200 pages, detail how an environmental anomaly involving the cold-sensitive gizzard shad tested the plant in unexpected ways.
Bruce Power, the plant’s operating company, declined a broadcast interview but later issued a written statement without addressing specific questions from CBC News.
An investigation by Bruce Power determined that the plant faced “a novel environmental event,” while Canada’s nuclear regulator described an unprecedented influx of gizzard shad that overwhelmed the plant’s fish defenses. Another internal investigation highlighted that the fish incidents in February 2025 posed a significant challenge to reactor safety.
According to David Novog, a professor specializing in nuclear safety, a challenge to reactor safety signifies a reduction in the effectiveness of defense mechanisms, prompting nuclear power stations to shut down as a safety precaution.
Former Bruce Power principal scientist Douglas Boreham emphasized that while the plant’s operations were impacted by the fish event, there was no direct risk to reactor safety as the systems responded as designed.
A report by the Canadian Nuclear Safety Commission outlined the potential repercussions of the fish die-off incident in February 2025, which disrupted cooling systems for two reactors at Bruce Power, leading to the shutdown of Unit 2 and power reduction at Unit 1.
The scale of the fish event was massive, with Bruce Power estimating around 8.1 million gizzard shad near the plant on a single day in February 2025. Severe winter conditions and ecological factors led to the fish congregating around the warmer water discharged by the plant, resulting in a large number of fish deaths.
The incident at Bruce Power underscores a broader issue of environmental challenges disrupting nuclear plant operations globally. Similar events affecting cooling systems have been reported in other countries, highlighting the need for adaptation to changing environmental conditions.
Bruce Power’s investigation identified deficiencies in real-time environmental monitoring and an “organizational failure” to address emerging issues related to changing environmental conditions. The company has since allocated significant resources to mitigate future risks and enhance monitoring and prevention measures to safeguard against potential disruptions.
In response to the incident, Bruce Power has implemented various measures, including physical barriers, acoustic deterrents, and advanced monitoring systems to prevent a recurrence of the fish event. These steps are crucial as nuclear plants play a vital role in providing low-carbon electricity amidst the challenges posed by climate change.
The incident at Bruce Power serves as a reminder of the importance of proactive measures to ensure the continued safe and reliable operation of nuclear facilities in the face of evolving environmental conditions.