WILLIAMS LAKE, B.C. — B.C. officials said 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 said the sediments exceed guidelines and contaminated sites regulation standards for copper and iron.

The test results come as many locals and First Nations raised concerns about how fish in the area will get impacted by the Mount Polley tailings pond spill, which released 10 million cubic metres of waste water and 4.5 million cubic metres of silt into Polley Lake.

The total volume is equivalent to 5,800 Olympic swimming pools.

The findings are based on samples of silt taken Aug. 10 near the mouth of Hazeltine Creek and near Raft Creek. Much of the waste poured from Polley Lake into Hazeltine Creek and flowed down into Raft Creek and Quesnel Lake.

Environment Minister Mary Polak said the area is considered contaminated under provincial regulations and Imperial Metals, the company that owns the breached pond, must show the government how it will address the situation.

“They will have to present to us a plan for how they would address that,” said Polak. “In terms of the specifics, that will all unfold as the plans are put in place and reviewed by our staff and with First Nations.”

Polak said Imperial Metals must assess the areas affected by the spill before determining what, if any, cleanup approach can be used.

“They would have to take a look at the site itself and then specifically design what is possible and what is going to work well for that area,” she said.

She said it is still unclear what can be done to clean up the mess until more assessments are done.

“We don’t know the answer to what’s possible and what’s the best approach environmentally until there’s more work conducted,” said Polak.

But she said there may be a chance the government will force Imperial Metals to scoop out all of the toxic sediment, though that hinges on future assessments.

“If that’s what is most environmentally appropriate, then that’s what they would be required to do,” Polak said.

The Ministry of Environment said it is still too early to determine what kind of harmful effects the sediment could have on aquatic life.

Lana Miller, an official with the ministry, said copper could impact the reproduction, growth and behaviour of fish.

“The effects that we will see on higher organisms will probably come through the copper moving through the food chain,” she said.

Miller said more tests need to be done before authorities can understand what exactly will happen to fish and other wildlife in the area.

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.

-By Steven Chua in Vancouver with files from Paola Loriggio in Toronto.