Blue-green algae on the rise in St. John River, says UNB researcher

·3 min read
A bloom of blue-green algae picked up by researchers. (Submitted by: University of Alberta - image credit)
A bloom of blue-green algae picked up by researchers. (Submitted by: University of Alberta - image credit)

An associate professor of biology at the University of New Brunswick is warning residents about blue-green algae popping up along the St. John River this summer.

Janice Lawrence says mats of cyanobacteria will probably start lifting off the river bottom and washing ashore any day now.

"That's when they become dangerous," said Lawrence, who has been studying blue-green algae along the St. John River for the past three years.

The warning comes after the death of two dogs in Grand Lake, N.S. last month. The dogs' deaths appear to be linked to cyanobacteria, also known as blue-green algae.

Photo: Submitted
Photo: Submitted

In 2018, two dogs died while swimming at Carleton Park in Fredericton. A third dog died after swimming in the river near Hartt Island RV Resort, 14 kilometres west of the city.

"When they [mats] lift up off the bottom and float to shore, that's where there's potential contact from dogs and anyone else wandering the shoreline," Lawrence said.

What is it?

Blue-green algae are photosynthetic bacterial organisms naturally found in rivers, lakes and wetlands. The algae grow in warm conditions, when water levels are low and produce different toxins that can affect the brain.

They can also produce toxins that damage the liver.

Researchers are still trying to figure out what cyanobacteria looks like, as it comes in many forms and colours.

While cyanobacteria is commonly blue-green in colour, surface blooms can also be green, red, brown or yellow.

Benthic mats, which can form along the bottom of lakes and rivers, can look like clumps of vegetation that may appear black, brown or dark green in the water.

When washed up on the shore, they can be brown or grey once they have dried. They can also be attached to rocks or aquatic vegetation.

Where it's found

This year, Lawrence is studying why blue-green algae prefers one area of the river to another.

Traces of cyanobacteria have been found along the entire length of the river, but most areas are fairly safe.

Lawrence said the stretch of water between the Mactaquac Dam and Fredericton to the east seems to be a hotspot for the toxins.

In 2010 a Labrador puppy died from blue-green algae toxicity after swimming in the St. John River below the Mactaquac Dam in the Island View area.

"For the most part, the river is safe to go recreate," she said.


Public Health sent out an advisory at the end of June warning the public about the risk of blue-green algae.

"Algal blooms can be unpredictable, so it is important to always check the water before entering and to avoid swimming in areas where there are visible blooms or mats," said Dr. Jennifer Russell, New Brunswick's chief medical officer of health.

Lawrence is advising people to observe the shoreline and to monitor their animals and themselves in the area.

"Keeping a good eye, that's the best thing you can do," she said.

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