A new plan from Canadian Prime Minister Justin Trudeau may begin phasing out net-pen farming in British Columbia by 2025.

Net-pen farming involves raising thousands of fish in large nets suspended in the open ocean. Most supermarket salmon comes from these types of cold-water aquaculture farms in places like Canada, Norway and Chile. The practice is controversial because, like industrial livestock operations on land, the animals’ excrement pollutes the nearby environment and leads to infestations of sea lice that can spread to wild fish populations, among other problems.

Beyond eliminating net pens, the plan also calls for Canada’s first-ever Aquaculture Act, meant to ensure the environmental sustainability of the larger fishing industry. Details of that act haven’t been announced yet.

Salmon Farming Hurts the Environment

Farmed salmon in net-pens are jammed into crowded underwater cages and doused with antibiotics, disinfectants and other chemicals (Burridge L 2010). There, they even feed on young wild salmon, as one biologist showed in GoPro footage captured from inside a net-pen, as we reported back in 2016 (Salmon Farm Sickness Caught on Video).

These salmon are also usually fed diets high in less-healthy vegetable oil additives.

A typical British Columbia farm has 10 to 30 net-pens, according to the non-profit Fraser Riverkeeper. Each net-pen contains tens of thousands of salmon packed tightly together.

Those hundreds of thousands of fish generate tons of waste that blankets the surrounding seafloor. Fish feeds and materials used to decontaminate equipment can also elevate seawater concentrations of metals like zinc, copper and mercury, as well as nitrogen, phosphorus and carbon (Burridge L 2010, Brooks R 2010). Those contaminants work their way into local food chains, with potentially harmful results. Copper could harm crustacean communities near net-pens, for example, and zinc has been shown to have adverse effects on algae and some species of marine worms (Burridge L 2010). One study found elevated mercury levels in rockfish living near salmon net-pens, for example (deBruyn AMH 2006).

Packing all those fish together often leads to sea lice infections, too. And once an infestation takes hold in a net-pen farm, it can also spread to wild populations, endangering their health.

Also, salmon commonly escape from these farms and swim into the open ocean, where they compete with wild fish for resources and spread diseases (Naylor R 2005). In 2019, a fire at a British Columbian net-pen farm let some 21,000 salmon escape, according to the CBC. The incident prompted worries from local indigenous tribes that wild salmon populations could suffer.

An End to Salmon Net-Pens?

British Columbia won’t be the first to enact legislation aimed at net-pen farms. Washington state passed a law in 2018 demanding that non-native net-pen farms be phased out in the state by 2022. That law followed an incident where a net-pen collapsed entirely, allowing as many as 300,000 Atlantic salmon to escape into the Pacific.

Trudeau instructed his fisheries minister to begin drawing up a plan to gradually eliminate Canada’s net-pen aquaculture industry, part of a larger move to protect the nation’s oceans and rebuild its fisheries. The move comes after years of advocacy by First Nations tribes and scientists against net-pen farming and its associated impacts.

In place of the net-pen farms, fisheries may move to closed containment systems, either on land or in the water. These farmed fish operations feature impermeable barriers and treatment systems to help keep waste from leaching into the environment. But because such operations have higher overhead, they probably won’t replace net-pens to a significant degree.

These farmed fish also still likely won’t deliver the same nutritional value as wild-caught salmon, which are less fatty overall and can deliver more favorable ratios of omega-3 to omega-6 fatty acids.

Why Wild Salmon Is Better Than Farmed

As we recently reported (Wild vs. Farmed Salmon: What’s the Nutritional Difference?), farmed salmon are often fed cheap, vegetable-oil-rich foods filled with omega-6s rather than the omega-3s that wild salmon get from their natural diet. As a result, farmed salmon have a poorer balance of omega-3 to omega-6 fatty acids (Strobel C 2012). While omega-6s are important for our bodies, we already get plenty in a Western diet, and studies show too many of these fatty acids can negatively impact our cardiovascular health (Simopoulos 2008). Our bodies don’t make these essential fats, so we need to get them from omega-3 supplements or from our diet, chiefly from fish. These essential fatty acids play an important role in everything from heart and brain health to mood support.

Wild salmon have also been found to contain four times as much vitamin D as their farmed brethren. Vitamin D and D-rich foods are essential for our immune systems, and play a role in mental health, too.

Phasing out net-pen farming could help more consumers discover wild sources of seafood, potentially introducing consumers to healthier, and more environmentally-friendly, options. Canada is leading the way at the moment — it remains to be seen if other nations follow suit.


Brooks K., Mahnken C, Nash C, Chapter 10: Environmental Effects Associated With Marine Netpen Waste With Emphasis on Farming in the Pacific Northwest. Responsible Marine Aquaculture. 2010. https://books.google.com/books?hl=en&lr=&id=K7pt5N0RLGEC&oi=fnd&pg=PA159&dq=atlantic+salmon+net+pen+fisheries+waste+deposits&ots=vGNXJRt4aT&sig=ST8C26BOLeEbRSIsu7kHUALIS0M#v=onepage&q&f=false

Burridge L, Weis JS, Cabello F, Pizarro J, Bostick K. Chemical use in salmon aquaculture: A review of current practices and possible environmental effects. Aquaculture. 2010;306(1-4):7-23. doi:10.1016/j.aquaculture.2010.05.020

deBruyn AMH, Trudel M, Eyding N, et al. Ecosystemic Effects of Salmon Farming Increase Mercury Contamination in Wild Fish. Environmental Science & Technology. 2006; 40(11):3489-3493. doi:10.1021/es0520161

Naylor R, Hindark K, Fleming IA, et al. Fugitive Salmon: Assessing the Risks of Escaped Fish from Net-Pen Aquaculture. BioScience. 2005;55(5):427. doi:10.1641/0006-3568(2005)055[0427:fsatro]2.0.co;2

Simopoulos AP. The Importance of the Omega-6/Omega-3 Fatty Acid Ratio in Cardiovascular Disease and Other Chronic Diseases. Experimental Biology and Medicine. 2008;233(6):674-688. doi:10.3181/0711-mr-311

Strobel C, Jahreis G, Kuhnt K. Survey of n-3 and n-6 polyunsaturated fatty acids in fish and fish products. Lipids in Health and Disease. 2012;11(1):144. doi:10.1186/1476-511x-11-144