Heat wave blamed for earlier and larger Alberta fish kill

·2 min read
Dead fish floating in Pembina River. The fish died due to the heat wave across Alberta that resulted in low oxygen in rivers and lakes, a provincial scientist says.  (Stephanie Coombs/CBC - image credit)
Dead fish floating in Pembina River. The fish died due to the heat wave across Alberta that resulted in low oxygen in rivers and lakes, a provincial scientist says. (Stephanie Coombs/CBC - image credit)

In late June, Albertan families took to lakes and rivers for some reprieve from the extremely high temperatures which hit 40 C in some parts of the province.

But for some, the relief of cold water also came with the putrid odour of dead fish, as hundreds were washed ashore on lakes and rivers across the province.

"We're certainly expecting when water gets hot, fish will be both heat stressed and oxygen stressed," explained Michael Sullivan, provincial fish science specialist for Alberta Environment and Parks on CBC's Edmonton AM on Tuesday.

Sullivan said fish kill — a natural phenomenon where fish die during hot weather — has been occurring in Alberta for years. High temperatures in water cause algae blooms that lead to an increase in photosynthesis. At night, the algae use up the oxygen resulting in low levels overnight that cause the fish to "bizarrely enough, drown," he said.

Typically, fish kill happens at the end of July in Alberta, Sullivan said, but this year it not only happened weeks earlier but also in greater numbers than before.

"It was really at the popular lakes; Wabamun Lake, Lac Ste. Anne, the McLeod River were notable for people reporting certainly large numbers of (dead) fish," he said.

Although Sullivan couldn't provide actual numbers of fish that drowned, he said they expect it to be "in the hundreds, if not thousands.

"That is a tiny proportion of the total fish population … there are literally hundreds of thousands and millions of fish in Alberta," he said.

Although not an immediate cause for concern, Sullivan said the problem could progress as weather events become more extreme.

Stephanie Coombs/CBC
Stephanie Coombs/CBC

While there is no short-term solution for climate change, the amount of nutrients going into the river — which combined with heat are a major factor in deoxygenation of water — can be controlled.

Nutrients from fertilizer washed up from farms and from sewage in cities is a major cause of algae blooms. Over the years, due to efforts by advocacy groups and scientists in collaboration with municipalities, the run-off has significantly decreased, Sullivan said.

"The rivers have cleaned up a lot since the 1950s, 60s, 70s, where these kills were massive. The North Saskatchewan River had no oxygen in it for some years with very few fish left," he said.

Since then, fish populations have restored dramatically, which is why when fish kills happen now, Sullivan said people actually notice.

"It's sort of a glass-half-full kind of story," he said.

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