Yellowknife

A naturally forming ice dam caused water to leak into and overflow a toxic gold tailings pond in Yellowknife, Northwest Territories on May 14. The water is now draining back into the creek, which feeds to Back Bay on Great Slave Lake a few kilometres downstream. Great Slave Lake is the second largest lake in the Northwest Territories, the deepest in North America, and the 9th largest in the world. 

Originally one of the most pristine bodies of water in the world, the lake water was rendered undrinkable by pollution from the mining industry. The people of Yellowknife have sourced their water elsewhere, until now. City officials have tabled a proposal to source Yellowknife's drinking water from Yellowknife Bay, which encompasses Back Bay, connected to the recent leak.

The Giant tailings hold the toxic byproducts of decades of gold mining, including tonnes of dangerous arsenic trioxide. The gold roasting process that produced seven million ounces of gold began in the 1940s at the city’s Giant gold mine, and was discontinued in 2004. The gold deposits were contained in arsenopyrite mineral formations, necessitating the separation of gold from arsenic, leaving 237,000-260,000 tonnes of highly toxic, water soluble arsenic trioxide dust, stored in 15 underground chambers a few hundred metres from Great Slave Lake.