N.W.T. waters return to normal after record concentrations of metals found in summer

After a summer that saw record-high water levels and even higher concentrations of metal in two N.W.T. rivers, water testing is showing a return to normal, and officials are anticipating a limited impact on local wildlife.

In the early fall, the territorial government released the results of water testing that showed levels of arsenic and other metals more than double previous records.

The results followed a sudden and late spring melt that caused record-high water levels on many N.W.T. waterways, necessitating boil water advisories and even forcing the evacuation of some communities.

That rush of water also stirred up sediment, which created a chocolate-coloured plume in Great Slave Lake that posed challenges to boaters and fishers.

New data now shows that those elevated levels of sediment and metals largely "returned to their normal range" by August, according to a release sent Friday.

The short period of elevated levels are also expected to have minimal impacts on fish and other wildlife, as most of the metals stirred up by rising water remained attached to particles of dirt.

"Substances that are attached to dirt generally do not affect the health of bugs and fish," the release says.

"While the concentrations of several metals measured in July for the Hay and Slave Rivers, and in August for Great Slave Lake, exceeded ... guidelines for the protection of aquatic life, the metals found in highest concentrations were attached to small particles," says a backgrounder accompanying the release. "In this form, the metals are not easily absorbed by fish and other aquatic life."

""Healthy water is of the utmost importance to the N.W.T. and its residents," reads a quote attributed to Environment and Natural Resources Minister Shane Thompson in the release. "The data and information we have gathered suggests that impacts to fish are not expected."

The territorial government collects regular samples of water from N.W.T. through the summer months, with the assistance of community-based water monitoring programs.

The latest data comes from samples collected on the Hay and Slave Rivers and Great Slave Lake in August and September 2020.