In August 2014, the tailings storage facility of the Mount Polley copper–gold mine failed catastrophically releasing 25 million m3 of contaminated liquids and solids into the environment. This represents the second largest mine spill in the world. Most of this material flowed down Hazeltine Creek, eroding a further 1 million m3 of topsoil and channel material, and was deposited in Quesnel Lake, a large, deep lake that is important for migratory Pacific salmon and other resident fish species. Since the spill, researchers and students associated with UNBC’s Quesnel River Research Centre (QRRC) and collaborators from Fisheries and Oceans Canada, University of British Columbia and University of Lethbridge have been investigating the effects on the receiving aquatic environment, especially Quesnel Lake and Quesnel River, which flows out of the lake and joins the Fraser River at the community of Quesnel. Concentrations of copper on material at the bottom of Quesnel Lake in the area impacted by the spill are elevated relative to local background values and exceed federal sediment quality guidelines for the protection of aquatic life. This lake bottom material ‒ which is predominantly deposited tailings ‒ is mobile and is resuspended into the water column due to physical processes within the lake. The resuspended, contaminated sediment and tailings are subsequently exported to downstream Quesnel River, mainly during the winter and early spring flows. These findings have implications for this important aquatic ecosystem.