As the spring thaw dredges odours from the depths of Yellowknife’s Niven Lake, blame raw sewage and a warming planet for intensifying the lake’s natural musk.
Emily Stewart was a PhD student at Queen’s University when she heaved a boat over the wooden barrier at Niven Lake before piloting through the reeds to sample the clearer water at the centre.
It was late July in 2015, and the lake’s notorious smell had faded for the summer.
“It smelled a bit marshy,” she said. “It had a productive lake smell.”
What Stewart means when she calls the lake “productive,” and what the City of Yellowknife means when it refers to Niven Lake’s “natural anaerobic processes,” is that microorganisms in the lake eat its living material and release gases like methane and ammonia while they do it.
Stewart, now a postdoctoral fellow in northern research at York University, said a combination of the lake’s past as a sewage lagoon and the ongoing impacts of climate change may intensify its productivity – and smell – today.
Niven Lake began its tenure as a sewage lagoon in the late 1940s, when increasing mining activity around Yellowknife drew miners, and their waste, to the area.
Raw sewage flowed into Niven Lake for decades, until researchers in the mid-1970s measured its contamination and recommended that Yellowknife find a different place to dump its sewage. The City built its current system, Fiddlers Lagoon, in 1981.
Years of sewage flowing into Niven Lake acted as fertilizer, increasing its productivity and causing plant life to bloom.
Stewart says it’s unlikely Niven Lake will ever completely recover, but her research gives a clearer picture of what the lake would look like if not for human activity.
“Niven probably wouldn’t return to pre-impact conditions because a lot of other things have also changed since Niven was a sewage lagoon. The biggie would probably be climate change,” she said.
Stewart said she was surprised to learn the largest jump in the lake’s productivity came a decade after Yellowknife started treating its sewage elsewhere.
“The timing of that seems to have corresponded with regional climate warming,” said Stewart. “The added stressor of climate warming might be exacerbating the recovery of Niven.”
Stewart didn’t speculate about what rising temperatures could mean for Niven Lake’s smell in the future.
So far, this year’s smell has been comparatively tame. The lake was especially pungent in 2018, when elevated flows through the drainage system connecting it to Frame Lake caused water to pool and the smell to linger through the winter.
Niven Lake residents reported severe headaches from the vapours at a public meeting held to address the issue.
Yellowknife public works expects a normal cycle this year, with peak smell occurring when ice recedes in the spring and water freezes in the fall.
“Although odours from the natural anaerobic processes of the lake may occur in transition months, the smell is not expected to linger this year,” a spokesperson for the City of Yellowknife said in an email.
The gases behind the smell are locked away by winter ice or free to dissipate in the summer.
That means Niven Lake was at its least aromatic when Stewart was “up close and personal” taking samples.
“I’ve worked in sewage lagoons before,” she said. “Niven seems like a relatively pleasant place to be, compared to some of the other lakes.”