It draws people from all over Alberta and beyond for its fish, provides a playground for thousands each summer, and supplies the town of Slave Lake with its drinking water. Lesser Slave Lake (hereby referred to as the lake) is vitally important to this region and some people are wondering how much longer it can be taken for granted.
Roderick Hazewinkel is a freshwater biologist with Alberta Environment. At the behest of the Lesser Slave Watershed Council, he is conducting a series of tests on the lake to determine its history and health. He tells The Leader it is not as pristine as many people would like to believe.
“This was initiated by the watershed planning group mostly in relation to how green the lake gets in the summer,” he says. “The lake gets very green in late July or mid August. It actually looks like grass clippings floating on the water.”
It’s common name is bluegreen algae but according to Hazewinkel, it is not a true algae. Rather, it is a cyanobacteria. It’s iridescence can be pretty to look at but it doesn’t not bode well for the lake. Hazewinkel’s studies suggest that bluegreen occurrences are likely to increase in the future.
Starting in October 2005, sediment samples have been retrieved from the lake bottom to look back in time. Anecdotal evidence says the lake used to be much clearer and looking at sediments can prove or disprove that.
“We drop a tube into the sediment, pull it out, and we have layers of sediment to analyze. At the top, they would be very recent. At the bottom, they could be as old as the lake.
“It says the lake has been getting more productive, more green since somewhere between (the year) 1750 and 1800. It happened gradually but within the last 50-100 years, the rate at which the lake becomes greener has really taken off.” Being greener simply means the lake has too many nutrients. Phosphorus is the biggest culprit. Found in fertilizers and body waste, phosphorus promotes the growth of bluegreens. The recent spike in nutrient levels is likely due to livestock operations.
“Cows produce about 15 times more phosphorus than we do and waste from livestock is not treated. If you get a big flood like you did in 1996-97, that gets washed into the lake.”
Considering there are 10 cows and hogs for every person in Alberta, it’s easy to see how fecal run-off can pollute watersheds. However, Hazewinkel is slow to put all the blame on farmers. He suggests that animals be kept away from open watercourses, but other factors may have played a part in the lake’s nutrification.
“With climate warming, lake behavior changes how it mixes. How the bottom waters turn over with the top. A lot of phosphorus in the lake is recycled from year to year. Once it’s in the sediments, it doesn’t just stay there. It can be stirred up. It has something to do with the chemistry that happens in low oxygen conditions at the bottom, phosphorus just builds up over the years.
“Another possibility is that it has something to do with the trapping industry. A lot of beavers were taken out of the catchments around that time, around 1800. Eventually, the beaver dams started to fall apart and all the nutrients that were being held back (got) washed into the lake.”
Hazewinkel lends less credence to the last theory. He suspects that beaver populations have recovered in the last 100 years yet nutrient levels in the lake continue to climb. He believes this trend will continue. The next phase of Hazewinkel’s project will examine diatoms in the lake. Diatoms are fossilized remains of tiny plants. They accumulate in the sediment and can provide hard numbers for how nutrient levels affected the lake in the past.
“You can use these things to actually reconstruct nutrient levels in the lake from 200 years ago. You can decide on targets for nutrient loading plans. That should be happening in the next year or so. “
The big picture is not completely in focus yet, but Hazewinkel says the community as a whole will eventually have to decide what to do about the lake’s increasingly poor health.
“There is always a trade-off with the economy and the ecosystem. When the lake is very green, these cyanobacteria can produce toxins that cannot be removed by boiling. Basically, if that happens, they would have to shut down the water supply for potentially weeks at a time.”

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