Invasive weed that’s ‘choking’ Alberta lake at risk of spreading
A tuberous weed known for pretty pink flowers is strangling a rural lake, alarming property owners concerned that without prompt intervention the invasive species will spread across Alberta.
“It is choking the lake completely,” said Gaston Savoie, whose property at Isle Lake, about 90 kilometres west of Edmonton, has been dominated by flowering rush. “Once it hits the North Saskatchewan River, then what?”
The weed, marked by an umbrella-shaped bloom and prolific root system, has grown out 15 metres past Savoie’s shoreline, hindering lake access and overwhelming the native bulrushes.
He’s among the dozens of community members waging war on the flower, which the province designated as a noxious weed in 2010.
“If it’s left untreated, there’s a risk it can spread to other lakes in the area, so we take that concern very seriously,” said Matt Dykstra, spokesman for the Ministry of Environment and Parks.
The plant used to be coveted by gardeners to beautify home ponds, but was mishandled and took root in 20 locations across Alberta, he said. It has been identified in Chestermere Lake near Calgary, the Bow River, the South Saskatchewan River and the Sturgeon River, which feeds Isle Lake and eventually flows into the North Saskatchewan River.
Other provinces aren’t immune. Saskatchewan has identified the weed in one location, while British Columbia has also reported a few isolated problem spots.
At this point, Isle Lake is dealing with the most significant infestation in Alberta, Dykstra said.
“Despite legislation to stop possession and import, we still intercept plants from stores.”
A collection of homes surround Isle Lake, a popular site for cottages, camps and recreational water sports, including the unincorporated community of Lake Isle. Local residents are concerned the weed is affecting fish and bird life, while also obstructing docks from accessing the lake.
But their chief concern is the weed will continue to spread and make its way into other lakes and rivers, said Sharon Beadle, who retired to the area in 2014.
Flowering rush has matted her shoreline after futile attempts to dig out the plant by hand. Root fragments left in the water grow easily, making it difficult to kill the species entirely through digging.
The province had planned to spray the lake with a diquat herbicide July 18, a move that would have started a years-long process to treat the lake. Destroying the plant can take up to five years of seasonal sprays, conducted at specific times to protect spawning fish populations.
The plan was cancelled after community members raised concerns about the chemical, Dykstra said.
“Primarily there were some concerns from First Nations groups that we had to take into account. Before we take the step of using an aquatic herbicide, we chose to take some more time and engage with folks,” he said.
After treatment, people are asked to avoid swimming in the lake for 24 hours and must not consume the water for five days, including for irrigation.
The Alexis Nakota Sioux Nation is located about 20 km downstream from Isle Lake on Lac Ste. Anne.
“Our people drink the water,” said consultation manager Duane Kootenay. “We don’t know much about this (herbicide) ... only that it’s the only proven chemical to treat this plant.”
His community was notified of the plan to spray about 18 months ago, but Kootenay said they weren’t consulted properly and remain concerned about the herbicide’s long-term effects.
“We have people who still practise the culture, they harvest the animals, medicinal herbs. This affects our treaty rights,” he said.
“Mother Nature has an equilibrium and sometimes mankind does too much in an area and Mother Nature tries to correct that in its own way. As far as we know, maybe that’s what the flowering rush is all about.”