Fish Event at Bruce Nuclear Plant Highlights Climate Vulnerability

Newly obtained records reveal that a "novel environmental event" involving millions of gizzard shad challenged reactor safety at the Bruce Nuclear Generating Station near Tiverton, Ont., in February 2025, according to reporting by CBC News.

On Feb. 1 and Feb. 13, 2025, cold-sensitive gizzard shad congregated in the warmer thermal discharge waters of the plant to escape freezing Lake Huron temperatures. In a March 2026 report to Fisheries and Oceans Canada, Bruce Power estimated that on one single day, 8.1 million fish were present near Bruce A. The volume of fish overwhelmed cooling system defenses, forcing Bruce Power to shut down Unit 2 and reduce power at Unit 1. A prior event on Feb. 1 also affected cooling at Unit 4.

An investigation concluded in June 2025 that these events "challenged reactor safety." David Novog, a McMaster University professor and Canada Research Chair in Nuclear Safety, told CBC News that such a challenge typically implies a defense layer was taken offline or reduced in effectiveness, requiring a shutdown. However, Douglas Boreham, a professor at the Northern Ontario School of Medicine University and former principal scientist at Bruce Power, stated the reactors responded as designed and that, in his opinion, there was no risk to reactor safety.

In a May 5, 2025, correspondence, the Canadian Nuclear Safety Commission (CNSC) warned Bruce Power that the event could have potentially resulted in the shutdown of all four Bruce A units. The CNSC later detailed these consequences in an April 2026 report prepared for the International Atomic Energy Agency.