B.C. officials say sediment discharged from a tailings pond that spilled mining waste in the Cariboo region is not toxic for humans but may harm aquatic life.
The province says the sediments exceed guidelines and contaminated sites regulation standards for copper and iron.
Environment Minister Mary Polak says the area is considered contaminated under provincial regulations and the company responsible for the spill must submit a plan detailing how it will address the situation.
Polak says Imperial Metals must assess the areas affected by the spill before determining what, if any, cleanup approach can be used.
She says it is still unclear what can be done to clean up the mess until more assessments are done.
The tailings dam at the Mount Polley gold and copper mine failed last week, sending millions of cubic metres of water and silt spilling into lakes and rivers in a remote area about 600 kilometres northeast of Vancouver.
Hundreds of people were ordered not to drink or bathe in their water as the company that owns the mine, Imperial Metals (TSX:III), started cleaning up.
Initial test results came back within drinking-water and aquatic-life guidelines, prompting the local health authority to partially lift the water ban.
But there has been concern about the impact on fish that live in or pass through the affected lakes and rivers.
The chiefs in two First Nations communities in the area have said their residents don't trust the government's claims that the fish are safe, so they've opted not to harvest salmon in what would normally be the busiest time of the year.