How? By causing the creation of a neurotoxin, methylmercury which bioaccumulates and enters the food supply relied upon by local communities.

Mercury is naturally present in river bottom soil; when disturbed, it converts to toxic methylmercury, which that bioaccumulates through the food chain. 

Research by Harvard University on dozens of dams proposed or under construction in Canada finds that 99% of them expose people who eat foods from the rivers to unacceptable levels of methylmercury. Calder et al., Future Impacts of Hydroelectric Power Development on Methylmercury Exposures of Canadian Indigenous Communities, Department of Public Health, Harvard T.H. Chan School of Public Health and Harvard John A. Paulson School of Engineering and Applied Sciences, 2016. (Download below) Also in 2016, the Nunatisavut Government published Lake Melville: Anativut, Kanuittailinnivut Scientific Report. This study was done by “Independent research by a team of expert scientists from Canada and the United States carried out extensive field programs and data synthesis using state-of-the-art research methods to develop an authoritative understanding of key processes and dynamics in the estuary. The primary research objective was to understand how Muskrat Falls [Nalcor hydropower facility] would impact the Lake Melville ecosystem and Inuit who depend on it for their well-being. A secondary objective was to anticipate the potentially compounding impacts of changing climate. These findings create a robust baseline understanding of the Lake Melville ecosystem and potential future changes, particularly with regards to two main areas of concern for human health: 1) methylmercury in country food and 2) ice and ice-based travel.

The project was co-led by Tom Sheldon, Director of the Environment Division Memorial University of Newfoundland. It address how flow alteration due to Nalcor’s dams will affect the physical processes in the river and lake environment, and that “continued detailed monitoring” is critical. There appears to be no such plan in place.

Methylmercury contamination can persist in some species for thirty to fifty years – requiring local communities to abandon the wild foods they have relied upon for millennia, or to risk the harmful effects of mercury poisoning.