Potentially toxic cyanobacteria blooming early in St. John River, expert says

When aquatic botanist Meghann Bruce did her usual spring visit to a hotbed of cyanobacteria production in the Fredericton area in May, she was surprised to see it was already in full bloom.

Normally, she wouldn't see those conditions until later in the summer. 

"There were already mats washing up on shore as I arrived at the boat launch, and we already had a thick carpet-like bloom here that I normally wouldn't see for at least another month, if not six weeks," said Bruce, an aquatic botanist and research scientist with the Canadian Rivers Institute.

She suspects the early bloom was a product of an inconsequential spring snowmelt.

It's difficult to say what such an early bloom will mean for conditions this summer, Bruce said, because there are too many factors at play to make predictions. 

It's also important to remember that the mere presence of cyanobacteria isn't cause for concern since they're commonly found in the environment, she said.

"Cyanobacteria are ubiquitous. You can find them in the soil. You can find them on rocks. They're on the bottom of your shoes. They're not hard to find. But if we see them growing, forming a carpet-like mat, especially in an area like this where we know it's a previously recorded toxin-production site, then we would call that a bloom."

The problem is that cyanobacteria can produce a neurotoxin called anatoxin-a, which is also known as blue-green algae — although Bruce doesn't like to use the term because cyanobacteria can also be sewage brown or bright yellow. 

Cyanobacteria usually form on the bottom of waterways and clump together to form surface blooms or benthic mats. Surface blooms can look like scum, foam or paint streaks, while benthic mats are clumps of brown or dark green vegetation. 

As the mats mature, they become buoyant and float to the surface, where they can be carried by the water for several kilometres. 

While broken pieces of the mat often resemble sewage, dogs are attracted to it. The toxins it contains can cause skin irritation and ingesting them can be lethal. 

In 2018, three dogs died as a result cyanobacteria after swimming in the St. John River in the Fredericton area.

Another dog died in the same area in 2019 within minutes of coming ashore. 

All the dogs died after swimming In the St. John River below the Mactaquac Dam.