Hot weather and warm water make an excellent breeding ground for green algae to bloom. A large bloom can be so thick so as to resemble pea soup. While not directly dangerous to fish, animals, and humans, a large bloom can lead to a much more dangerous form – blue green algae.
“Blue green usually happens after we get these large green algae blooms,” says Alberta Fish and Wildlife biologist David Derosa. “The green algae is the pea soup kind of stuff. As it deteriorates and dies, it consumes oxygen and then you start seeing the opal coloured algae. That’s the blue-green. That’s the stuff ourselves, pets, and our water intakes have to worry about.”
Derosa says that blue greens are already confirmed in some of Alberta’s lakes. The algae is a single cell cyanobacteria that produces a microcystic toxin. It proliferates in water with a high nitrogen and phosphate content.
“Lesser Slave Lake is very high in (phosphates) to begin with,” says Derosa, “the west basin being higher than the east basin because it’s shallower and has more major rivers.”
“It’s the time of year, especially with this hot weather, and we’re starting to see some fish kills,” says Derosa. “Snipe Lake had a minor fish kill, Sturgeon Lake had a minor kill. We’re keeping a close watch on some others, including Utikuma and Little Utikuma (and)south of Wabasca.”
Higher than normal rainfall last year and earlier this summer have exacerbated the situation.
“What that does is draw nutrients from the watershed and bring them down to the lakes,” Derosa explains. “Most nutrients would have settled very quickly and mostly in that west basin. But the lake itself still looks pretty good for this time of year compared to other lakes in the region. Hopefully we won’t see the same situation as in 1999.”
That was when Slave Lake’s water supply was contaminated with blue green algae. Residents were forced to boil water to ensure its purity. Consuming water contaminated with blue greens causes muscle twitching, photosensitivity, and loss of coordination at the onset of poisoning. Fish and livestock die fairly quickly from respiratory failure. Humans are not immune and actually increase the rate at which nutrients enter Lesser Slave Lake.
“When you have natural erosion, land development, agriculture, forestry, all these land disturbances, you increase the rate at which phosphates enter the water,” Derosa warns. “We’re still early in the development stages of our watershed so most of the phosphates we’re seeing are from natural processes. Slave (Lake) in still in pretty good shape. It’s still very early though and we still have August to go through this season.”
If you see dead fish or suspect blue green algae, call Alberta Fish and Wildlife at 849-7108.
“If you see large blooms that you consider to be blue-greens, give us a call or give the health authorities a call. Generally, we'll go out and investigate the situation and tell the authorities if we find something."

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