The Parasite Problem Salmon Farms Can’t Get Ahead Of

Parasites aren’t just a nuisance for salmon farms, they can be a full-blown catastrophe for the farm fish and juvenile wild salmon that are migrating by. Around the world, efforts to prevent sea lice outbreaks on factory fish farms have driven the aquaculture industry into a global arms race of pesticides, chemicals, and treatments. British Columbia is no exception.

In B.C., two species dominate: Lepeophtheirus salmonis, the salmon louse commonly referred to as “Leps,” and Caligus clemensii, sometimes called the herring louse. Both are ectoparasites, feeding on the mucous, skin, and blood of fish. Leps are salmon-specific, while the herring louse can infect salmon, herring, and other species.

A large body of scientific evidence shows sea lice from fish farms can devastate wild fish health and populations.

Watershed Watch’s Stan Proboszcz

As sea lice outbreaks are a common problem on farms, the industry is required by DFO to monitor lice levels. Historically, B.C. salmon farming companies posted monthly farm lice levels publicly on their websites, a rare window into the operations of a largely secretive industry. But that’s changing for some of the big Atlantic salmon farming companies operating here in B.C.

Why Are B.C. Salmon Farming Companies Not Posting Their Lice Data?

Over the past year, major Atlantic salmon farming companies operating in British Columbia—Cermaq and Grieg Seafood—have reduced or stopped publishing lice numbers on their websites.

• Cermaq stopped posting publicly in August 2024, according to our friends at Clayoquot Action. Now they state on their website that they only report the numbers to DFO.
• Grieg Seafood last updated its numbers in September 2025, showing several sites with explosively-high salmon lice levels.
• Mowi, the world’s largest multinational salmon-farming company, last published lice levels for its B.C. farms in October 2025. Whether they intend to continue public updates remains uncertain.

Is this a trend toward secrecy? It certainly looks that way.

A before-and-after comparison of juvenile salmon after fish farm removal from the Discovery Islands.

Exploding Sea Lice Levels and No Consequences

Technically, salmon farms must keep average salmon lice levels below three motile lice per fish during the wild juvenile salmon outmigration window: March 1 to June 30. Farms are required to take action if they exceed this threshold, yet we are not aware of penalties ever being enforced.  

One of Grieg’s final public updates shows that in September, their Gore factory fish farm in the Nootka region of Vancouver Island was at a whopping average of 32 motile lice per fish. Is this why they’re not reporting? Because of massive parasite outbreaks on their farms?

One of the last reported monitoring results for parasitic lice levels at Grieg Seafood’s Gore salmon farm in Nootka Sound on Vancouver Island. 

Less Transparency Could Mean More Mass Mortalities of Farmed Fish and More Risk for Wild Salmon

Parasites on factory fish farms don’t just threaten wild fish. High sea-lice levels on farms can be linked to massive farm mortality events, like the recent 2024 die-off in Nootka Sound, where tonnes of farmed fish perished. This year, Cermaq experienced mass fish farm mortality events in their Clayoquot Sound sites. With die-offs this severe, the industry can’t even feed itself — never mind the world, as it likes to claim.

We believe this secrecy isn’t just about hiding information from the public. It’s about keeping potential investors and shareholders from seeing how bad things really are in B.C. The truth is blunt: B.C.’s salmon farming industry is a slow sinking ship. 

Regardless, all B.C. marine factory fish farms have to be out by 2029, according to a ban promised by the federal government. Help speed up their removal before they do more damage. Please take a second to remind your member of parliament to speed up the ban.

Photo: Tavish Campbell