I’m from northern Ontario, and in 2023, I studied how often healthcare providers were screening for elevated mercury levels in their patients — a study inspired by elevated mercury levels found in several of my fellow anglers and hunters.
Mercury is a naturally occurring toxin that bioaccumulates and biomagnifies within its host. In the context of toxicity to humans, we are looking at organic mercury — specifically, methyl mercury which is formed by the transformation of inorganic mercury by aquatic life. It can be initially found in the air, soil, and water before ending up in fish and, eventually, people. Elevated mercury levels in humans are on the rise in Canada, especially in remote areas where a higher consumption of fish occurs.
Acute and urgent exposure to methyl mercury can cause serious health issues. However, what the people should be mindful of is the chronic low dose poisoning which can cause kidney damage, liver damage, cognitive issues, and central nervous system damage. All of this sounds scary, but we do have guidelines available.
Anyone who is pregnant or may become pregnant and children under 15 should take extra precautions when eating fish. Mercury can impact the health of fetuses, babies, and children at lower levels compared to the general population.
The Canadian government, in partnership with Health Canada, has an equation for exposure assessment and acceptable fish intake. However, mercury levels differ from lake to lake, and from fish to fish, so we cannot assume one species of fish holds the same amount of mercury in every lake. There are helpful resources such as the Guide to Eating Ontario Fish. Because of the financial cost associated with surveys, and the vast number of waterbodies, data is not available on some lakes and rivers. Travel distance and available scientists are other factors.
In the study I conducted in the summer and fall of 2023, it was found that the majority of healthcare providers (midwives, doctors, and nurse practitioners) did not screen specifically for fish consumption in their patients.
So, what can we do? We do not have to stop eating fish, but perhaps people that eat fish should be more aware of the risks, eat fewer top predators such as salmon, trout, pike, and walleye, be aware of what lakes may have more organic mercury, and be more open about our fish consumption with health care providers.
We can also look at supporting healthcare providers in screening for high fish consumption, perhaps even look at exploring additional ways to help them navigate when to screen. At the end of the day, consuming fish is not only beneficial to our health in terms of nutrients, but also a way of life for many Canadians.
There are also numerous other toxins that anglers should also consider when eating fish, reminds Ontario Federation of Anglers and Hunters Fisheries Biologist Adam Weir. These include polychlorinated biphenyls, pesticides, and dioxins.
Unlike mercury which evenly distributes throughout fish flesh, these toxins concentrate in fatty flesh (especially salmon and trout) so anglers can reduce exposure by getting rid of the skin, cutting off fatty parts, and removing the flesh around the belly area.
Many people within the angling community have personal perspectives on fish consumption and exposure to contaminants like mercury, Weir noted.
“The opinions range from advisories being complete hogwash to individuals that have serious concerns about the health impacts,” he said. “What fish you eat and how much ultimately comes down to personal choices that are best for you and your family, and Ontario’s Guide to Eating Fish is available so you can make the most informed decision.”
Originally published in Ontario OUT of DOORS’ Fishing Annual 2025
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Peterborough, Ontario Canada K9J 8L5
Phone: 705-748-OFAH (6324)
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