Montreal

Bromont Lake gets rid of blue-green algae, as experimental treatment takes hold

Blue-green algae has plagued the waters of Bromont Lake for 50 years — and over the past decade, the municipality has been forced to intermittently close the lake to swimmers to try to contain it.

A chemical treatment was poured into the lake in November to trap the phosphorous that algae feeds on

Bromont Lake, in Quebec's Eastern Townships region, has been dealing with an abundance of blue-green algae for decades. (Radio-Canada)

Blue-green algae has plagued the waters of Bromont Lake for 50 years — and over the past decade, the municipality has been forced to intermittently close the lake to swimmers in an effort to contain it.

That may become a thing of the past, after Bromont decided to take a new approach to deal with the pesky problem.

Last year, the city spent $615,000 on an experimental treatment, and in November, 175 tons of a product called Phoslock was poured into the lake, located in Quebec's Eastern Townships region.

The experiment was carried out under the supervision of Philippe Juneau, a biology professor at the Université du Québec à Montréal, who said it appears to be working as planned.

"So far, we didn't see any [algae] blooms," and the beach has been open all summer, Juneau told CBC News.

"That's very promising."

Product traps phosphorous, which algae feeds on

Blue-green algae, also known as cyanobacteria, uses phosphorous to grow and expand its reach in bodies of water.

Phosphorous can be found in sediments already in the water, and it can also come into lakes via run-off from rivers or other sources of water.

Heat and a lack of oxygen in the water can also contribute to the growth of blue-green algae.

"Plants need phosphorous, so if you block the phosphorous that is available, the plant or the algae or the cyanobacteria cannot grow," Juneau explained.

Philippe Juneau, a biology professor at the Université du Québec à Montréal, said there have been no algae blooms in Bromont Lake so far this summer. (Radio-Canada)

Anne Joncas, president of a group of citizens working for the conservation of Bromont Lake and its basin, said the municipality began closing the beach due to an abundance of blue-green algae in 2006.

Since that time, "there's been an increased awareness about the importance of cyanobacterial issues in Quebec."

"It raised the alarm," she told Radio-Canada.

The algae can cause gastrointestinal distress and skin irritation for swimmers that come into contact with it.

It's not a magic solution, however

This is the first time the Phoslock treatment — which traps the phosphorous found in sediments that algae feeds on — is being used in Quebec.

This approach won't be the best fix for all lakes, Juneau said.

It works well in Bromont Lake because the phosphorous there is caused by sediments, he explained. In a lake where the main source of phosphorous is a river, it won't be as successful.

"You need to understand your lake. You need to understand that the phosphorous source comes from the sediment, and not from the external source," he said.

Since 2006, Bromont has been forced to intermittently close the beach at Bromont Lake in order to deal with a blue-green algae problem. It has remained open every day so far this summer. (Radio-Canada)

In the meantime, Juneau said people in Bromont are happy they can enjoy the water.

"People were swimming in the lake Saturday morning ... and that's something that we didn't see last year."

With files from Radio-Canada and CBC's Brennan Neill