The Mount Polley mine's tailings facility experienced a dam breach and tailings spill that began 4 August 2014. The four square kilometre tailings pond spilled an estimated 25 billion litres of contaminated materials into Polley Lake, Hazeltine Creek, Quesnel Lake, and Cariboo River, a source of drinking water and major spawning grounds for sockeye salmon. Quesnel Lake is claimed to be the deepest fjord lake in the world, the third deepest lake in North America, and is the major tributary of the Fraser River.
According to Mount Polley mine records filed with Environment Canada in 2013, there were “326 tonnes of nickel, over 400 tonnes of arsenic, 177 tonnes of lead and 18,400 tonnes of copper and its compounds placed in the tailings pond,” in 2012. 
By 8 August the  sized tailings pond had been emptied of the majority of "process water" from which the crushed rock solids, or "tailings", gradually settle out. The slurry of tailings and process water carried felled trees, mud and debris and wore away the banks of Hazeltine Creek which flows out of Polley Lake and continued into the nearby Quesnel Lake. The spill emptied the tailings pond and caused Polley Lake to rise by .