Thousands of farmed salmon perish in massive die off near Tofino

A harmful plankton bloom and poor water conditions caused large mortalities at three Cermaq salmon farms in northern Clayoquot Sound near Tofino, with up to 185,000 fish lost at one site. DFO says disease was ruled out; critics warn the die-off could affect wild salmon and the marine environment.

AI Comment from GPT 5:

Context from related LEO posts:

• In 2016, toxic algae were blamed for mortality at Cermaq’s Millar Channel and Ross Passage farms in Clayoquot Sound, with the hardest-hit site losing about 10% of fish. Clayoquot Action was monitoring the event. Toxic algae blamed for die-off at 2 salmon farms in Clayoquot Sound

• In 2019, three Cermaq farms near Tofino reported mass die-offs due to a harmful algal bloom; the algae’s rigid spines were noted as damaging gills. The post stated the bloom was partially related to warming ocean temperatures, and described mitigation steps (reduced feeding, upwelling). Tofino fish farms reporting mass die-offs due to harmful algae

• In May 2025, Northern Norway experienced high aquaculture mortality—up to 1 million fish—during a spring bloom dominated by Chrysochromulina and Phaeocystis, with authorities citing the bloom species and local currents; mortality later declined as conditions changed. Algal Bloom in the North: Up to 1 Million Dead Fish

• On Canada’s Atlantic coast, Mowi reported salmon mortalities in Newfoundland and Labrador, attributing repeated sea lice issues to climate-related factors such as prolonged warm surface waters, low rainfall/runoff, and weak wind-driven currents, with other events linked to thermocline inversion and low oxygen. Mowi blames climate change for latest salmon die-offs on Newfoundland's south coast

• A 2021 study found piscine orthoreovirus (PRV) in BC was introduced with Atlantic salmon farming and spread from farms to wild salmon, linking PRV to disease in farmed and wild fish. This provides context for the PRV concerns raised in the post. Farmed salmon virus source, amplifies disease transmission in wild salmon: B.C. study

Taken together, prior observations in Clayoquot Sound (2016, 2019) and internationally (Norway 2025) describe harmful algal blooms and gill damage consistent with the DFO’s attribution to water quality, environmental conditions, and a suspected biotoxin in this event. The Newfoundland post highlights other environmental stressors affecting salmon aquaculture elsewhere in Canada, while the 2021 PRV study provides scientific background relevant to pathogen-shedding concerns noted in the post.