Aerator that could restore fish in Yellowknife's Frame Lake turned on

An aerator recently began pumping air into the water of Frame Lake in Yellowknife, and the mining company that set it up hopes it could bring fish back to the long-dead lake as early as 2026. 

Rio Tinto, which operates the Diavik diamond mine in the N.W.T., installed the device in the summer and turned it on last month. Its purpose is to increase oxygen levels in the lake. 

The project fulfills Rio Tinto's requirement, laid out under its fisheries authorization, to compensate for habitat loss caused by Diavik's construction. It has faced numerous delays since it was first announced, due to COVID-19 pandemic and the 2023 wildfires. 

Sean Sinclair, Diavik's closure manager, said the company will monitor the aerator over the next two winters at least before taking any next steps. If everything goes as planned, he said, they could consider reintroducing fish in a year and a half.

"We would also have to go through some additional permitting steps prior to actually reintroducing fish," he said.

Frame Lake hasn't had fish in it since at least the 1970s. High arsenic levels from nearby gold mining operations have also made the lake harmful to human health for decades.

Gila Somers, an aquatic quality scientist with the territory's Department of Environment and Climate Change, says oxygen levels in Frame Lake are too low for aquatic life to survive.

In an email to CBC News, she explained that nutrient pollution in the water creates algae blooms that consume most of the oxygen. 

Sinclair said that every winter once there's ice on Frame Lake, the oxygen level in the water goes down to zero. That "obviously creates conditions that would not be sustainable for a fish population," he said. 

But Somers said that aerators  – like the one Rio Tinto has installed – could help restore Frame Lake.

"These devices work by moving the water and adding oxygen from the air, which helps increase the amount of dissolved oxygen that fish and other organisms need to survive," Somers said. 

"In southern Canada, they have been successfully used to improve water quality and prevent fish kills."

Sinclair said Rio Tinto has started a sampling program and will check how the aerator is functioning throughout the winter and the summer. He said initial results about its winter performance will come in the summer.

The aerator has a beacon light flashing on top for visibility.