A pike may look perfectly healthy to the naked eye and still be unfit for consumption. This is what the Cree of James Bay discovered after the La Grande hydroelectric complex began operations in 1971. Five rivers diverted, more than 11,500 square kilometres of boreal forest flooded— the project transformed their traditional fish into a source of mercury.
The culprit isn’t the power plant; it’s the water itself.
- Flooding 11,500 km² of forest released natural mercury from the soil in the form of toxic methylmercury.
- The pike, a Cree staple at the heart of their diet, accumulated neurotoxic mercury.
- Mercury levels returned to natural balances after 20 to 35 years, but new dam projects threaten to repeat the cycle.
The mercury that slept in the soil
When the hydroelectric reservoir was formed, the forest was flooded and the green parts of plants feed microorganisms that transform mercury into a form that can accumulate in living beings, methylmercury. In this form, mercury is neurotoxic and builds up in the aquatic food chain, notably in piscivorous fish such as the northern pike, the lake trout, and the yellow perch. Mercury was already there, buried in the soil for millennia. All it took was to cover it with water to wake it up.
The La Grande complex comprises five reservoirs. The developed basin has a total installed capacity of 10,800 megawatts, supplied by five reservoirs spanning a total area of 11,300 km², roughly the size of Qatar.
The rise in methylmercury production typically ends eight to ten years after flooding, due to the rapid exhaustion of readily decomposable elements in the soil and submerged vegetation.
The Cree, subjects despite themselves of half a century of monitoring
The development of the La Grande River complex’s reservoirs triggered mercury contamination in fish, especially those at the top of the food chain, such as the northern pike. The pike, in particular, held a central place in Cree traditional alimentation. Only one village had to be relocated for the project, but the social impact was considerable.
In response to the problem, an institutional reply eventually emerged. A mercury agreement was signed in 1986 between the Cree of James Bay, the Quebec government, and Hydro-Québec. Fish consumption guides for La Grande’s fish were produced in 1998, 2001, 2004, and 2013, according to exposure criteria established by the Cree Health and Social Services Board of James Bay. At the same time, a program directly measured mercury levels in the hair of residents in the adjacent communities, a simple and remarkably effective indicator of actual exposure.
Mercury did not wait for the dams to circulate in local bodies. After the discovery of elevated mercury levels in the blood of the Cree in the region, even before the Grande River reservoirs were created, local health authorities had already issued specific guidelines regarding fish consumption.
Two pike meals per month, no more, were recommended to families living near the most affected reservoirs. Today, in most of the modified areas of the La Grande complex, mercury levels in fish have returned to levels representative of the region’s natural environments, and the time has come to promote the health benefits of fish. Two new dietary guides, published in 2013, outline the nutritional value and health benefits of fish for northern residents.
The pike comes and goes, but the cycle can start again
One generation is enough for the levels to fall again.
Monitoring of reservoir fish showed that mercury levels in insectivorous species, such as the Arctic cisco, return to levels similar to those of natural lakes after ten to twenty years. In fish that feed on other fish, such as the yellow perch, the return to normal takes longer and typically ends after twenty to thirty-five years.
For the vast majority of fish species and altered habitats, the average mercury levels obtained in the most recent surveys allow consumption frequencies similar to those recommended for natural lakes, to the point that it was recommended to end the monitoring. But Cree territory has not finished being redrawn. The Grande-Baleine project, planned under the James Bay and Northern Quebec Agreement of 1975, would have flooded roughly 1,667 square kilometres of additional territory, proving that this mercury cycle, however transient, is not an isolated accident as long as forests continue to be flooded to generate electricity.
Sources: osti.gov | hydroquebec.com | techno-science.net
