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For what may be the first time ever, potentially toxic blue-green algae was discovered this summer in the Rideau River within Ottawa’s city limits.
The algae, whose scientific name is cyanobacteria, was identified in August off Nichols Island, near the Rideau Canal’s Long Island lock station north of Manotick.
Ontario Ministry of Environment staff collected samples and found “minor evidence of toxins.”
But since the algal bloom had already almost disintegrated, it posed no threat to public health, according to Ottawa Public Health.
Blue-green algae has been present in stretches of the lower Rideau waterway for at least the past three years.
This year, it first appeared in early August and was found throughout the watercourse from Kingston to Seeley’s Bay, said Ed Gardner, manager of environmental health for Kingston’s health unit.
But this summer’s appearance near the Long Island lock station was the first time officials here can recall an occurrence within city limits. Until now, reports have been so rare that they weren’t even tracked by Ottawa Public Health.
Blue-green algae is part of the natural system, and is always present in waterways. It becomes a problem when it grows in massive quantities, generating a bloom that can produce microcystins, a toxin that is harmful to human and animal health.
Such blooms used to be uncommon in Ontario, but have been occurring with greater frequency over the past decade or so. “Since the start of this new millennium, it’s gathered steam,” Gardner said.
It’s not clear what’s causing the proliferation of blue-green algae in the province, but increased human waterfront activity and a warming climate may be factors, he said.
“These things are always around,” Gardner said. “If you get enough sunshine and enough nutrients, then you get it.”
Not all cyanobacteria produce toxins. But the blue-green algae identified in the lower Rideau system this year was capable of doing so, Gardner said.
Swallowing water that contains blue-green algae can cause headaches, fever, diarrhea, abdominal pain and vomiting.
Swimming in it can cause skin rashes.
Though rarely fatal in humans — in part because it looks so repulsive that no one would drink large quantities — cyanobacteria has killed many dogs and livestock. And in Brazil, 69 people died in the 1990s after receiving dialysis with water taken from a reservoir that had cyanobacteria.
Prompted by growing complaints about proliferating algae in the Rideau watershed, a working group of officials from Eastern Ontario conservation authorities, Parks Canada, the ministry of environment, universities and health units formed an informal partnership last year to monitor the problem.
The group found that by August last year, 22 per cent of the lakes and rivers south of Smiths Falls that it monitored had various types of algae outbreaks, including some with toxic cyanobacteria.
The partnership did further monitoring this year, looking for hot spots, but is still compiling its results.
One problem is that most members of the public can’t readily distinguish blue-green algae — which despite its name can be any colour from olive-green to red — from regular, non-harmful green algae.
Early in its life-cycle, cyanobacteria looks like spilled paint in the water, said Gardner. By this time of year, the cells are starting to die and clump together.
“Then they’ll just go down to the bottom of the watercourse and you won’t see it anymore for a while.”
Blue-green algae is likely here to stay in the Rideau waterway, Gardner said.
“It would be very hard to get rid of blue-green algae once it’s here.
“We have a climate that’s generally getting warmer and we have more human habitation around those areas. All these things add up to more food for the blue-green algae.”
dbutler@ottawacitizen.com
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