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.
Although the storage vaults are contained in bedrock and sealed with concrete bulkheads, concerns remain about leaching of arsenic into groundwater. Since the 1990s, evidence has mounted of substantial seepage  from Giant Mine tailings ponds into the nearby environment.
Arsenic trioxide is considered carcinogenic, and may cause kidney and liver failure and pulmonary edema. A lethal dose  is only 120mg.
On May 14th, the dammed creek flooded, and water seeped through the tailings ponds and back into the creek.
First Nations Dettah Chief Ed Sangris said of the flood that, "if the mayor's not careful, he's going to kill everybody in Yellowknife because stuff like this goes on".
Last week, Public Works Canada couldn't say what was in the water or the tailings pond because the water was being tested. Water samples were expected back from the lab Thursday.
Two weeks have passed since the leak, yet federal officials are refusing to talk about their findings, raising concerns about a coverup of the severity of the contamination. A ccording to the CBC , none of the departments involved — the Aboriginal Affairs and Northern Development Department, the Department of Fisheries and Oceans, Environment Canada, and The Department of Public Works and Government Services — have come forward to talk publicly about what the water tests show.
"I think there must be a reason because if there were minimal concerns, they would have released the results of the water samples," Chief Sangris said.
According to Sangris, there is a conflict of interest within the Aboriginal Affairs and Northern Development Department, which is involved in both cleaning up the Giant mine site and simultaneously enforcing the environmental rules it must obey.
Minister John Duncan is responsible for approving the water licence and cleanup plan for the former mine.
Members of the community argue that a monitoring system independent from government is necessary to ensure the clean up is carried out in an accountable and transparent fashion. Currently, permits are issued to Aboriginal Affairs and Northern Development by Aboriginal Affairs and Northern Development. Sangris poignantly asks, "So who's monitoring the regulators?"
Shifting Yellowknife's drinking water source to Yellowknife Bay, which encompasses Back Bay, would require the city to install an arsenic treatment system in the water treatment plant. Given the flood that happened this week, do we have reason to be concerned about the safety of Yellowknife Bay as a drinking water source?
We'll keep you up to date as this story unfolds.