Samples of fish and sediment in the region of the Mount Polley mine tailings breach are being tested to determine longer-term effects of metals contamination on the local environment.
The B.C. environment ministry has also collected rainbow trout and lake trout tissue samples, with results expected by the end of August. Sediment and plankton samples are also being tested from the region near Williams Lake.
“The tailings liquid initially released from the impoundment moved very quickly through the system and was diluted greatly by the water in the lake, the Quesnel River and ultimately the Fraser River,” the environment ministry said in a statement.
“As such, the fish exposure was limited and not long enough for uptake into tissues. Combined with the fact that the water in Quesnel Lake meets drinking water guidelines, it is unlikely there will have been any short-term effects on fish in Quesnel Lake or downstream as a result of this event.”
Tourism operators remain open on Quesnel Lake and throughout the Cariboo region.
Environment ministry boat crews have been on the water since the breach Aug. 4, but only one dead fish, a rainbow trout, has been reported. It was collected by University of Northern B.C. researchers and turned over to officials Aug. 6.
Based on water quality test results, Fisheries and Oceans Canada has re-opened the chinook salmon fishery on the Quesnel and Cariboo Rivers.
The B.C. First Nations Health Authority is conducting its own tests on migrating salmon at the request of affected First Nations on the river system.
Water use restrictions have been lifted in most of the area affected by the Mount Polley mine tailings breach after health authority water tests confirmed the water is not a risk for drinking or bathing.
Interior Health lifted the water use ban on all areas except immediate zone of the tailings and water spill, including Hazeltine Creek, Polley Lake and 100 metres around the out of the creek at Quesnel Lake. The tests corroborate earlier samples tested by mine operator Imperial Metals.
The only sample that yielded metal contamination was one taken from an area with visible sediment near Hazeltine Creek, which was scoured out by millions of cubic metres of water and mine tailings.
“Results show slight exceedances of phosphorus and aluminum for drinking water and exceedences of copper, chromium, phosphorus and aluminum for aquatic life guidelines,” the environment ministry reported. “These elevated levels would be expected near an aluminum/copper mine.”