The impact of a catastrophic mine tailings impoundment spill into one of North America's largest fjord lakes: Quesnel Lake, British Columbia, Canada

On 4 August 2014, a catastrophic breach of the Mount Polley mine tailings impoundment released similar to 25Mm(3) of tailings and water and scoured an unknown quantity of overburden into the West Basin of Quesnel Lake. We document Quesnel Lake and Quesnel River observations for 2months postspill. Breach inflows raised Quesnel Lake by 7.7cm, equivalent to similar to 21Mm(3). The West Basin hypolimnion was modified immediately, exhibiting increased temperature (similar to 5 degrees C to 6-7.5 degrees C), conductivity (110 to 160S/cm), and turbidity (<1 to 200-1000 nephelometric turbidity units (NTU)). Cooscillating seiches moved West Basin hypolimnetic water both westward and eastward contaminating the Main Basin. Postspill, high-turbidity water propagated eastward (similar to 1cm/s), introducing a persistent similar to 20m thick layer below the thermocline and an similar to 30m thick layer at the bottom. The contaminant introduction, mobilization, and bioaccumulation may pose risks to resident and anadromous fish stocks, which support recreational, commercial, and First Nations fisheries.