Lake Winnipeg Blue-Green Algae

Lake Winnipeg is the 10th largest freshwater lake in the world and the 6th Great Lake in North America. It is almost 25,000 square kilometres in size and has a watershed of almost 1 million square kilometres. Although it is such a huge lake in surface area, it is relatively shallow with a mean depth of only 39 feet.

Lake Winnipeg Watershed map

Lake Winnipeg Watershed map

Unfortunately since the late 1990s, Lake Winnipeg has been acquiring another noteworthy distinction (not a desirable one) for being plagued each summer by large blooms of blue-green algae. It has been called the “Sickest Lake in Canada” by McLeans Magazine August 2009. It received even greater international attention in 2013 when the Global Nature Fund designated it the Threatened Lake of 2013, worldwide. In some years the blue-green algae blooms cover more than 50% of the lake’s surface and can be seen from satellite photos from space.
Blue-green algae is actually cyanobacteria which is a single-celled organism that obtains its energy through photosynthesis. The blue-green algae blooms appear on the surface of water as a scum that that often looks like a can of paint that has been spilt. Some of the blue-green algae blooms contain toxins that are dangerous to humans and sometimes lethal to animals. Microcystis is one type of cyanobacteria that can produce neurotoxins and hepatotoxins. Not all blue-green algae blooms contain toxins but it is impossible to tell by simply looking whether there are dangerous toxins present so caution should be used whenever there is any possibility of blue-green algae present.

Lake Winnipeg blue-green algae in satellite photo from NASA

Lake Winnipeg blue-green algae in satellite photo from NASA

Blue-green algae has always been present in aquatic systems but in recent decades has dominated the phytoplankton composition in Lake Winnipeg. Its growth has occurred due to the increase in the nutrients phosphorus and nitrogen that are flowing into the lake from numerous sources. Phosphorus and nitrogen come from human sewage, animal manure, chemical fertilizers and natural run-off from the land. The major emphasis in decreasing the blue-green algae blooms has been to decrease the amount of phosphorus that makes its way into the lake. Less effort is put on decreasing the nitrogen as some of the blue-green algae can “fix” nitrogen from the air when the supply in the water is diminished.

Lake Winnipeg blue-green algae at Pine Dock 2014

Lake Winnipeg blue-green algae at Pine Dock 2014

The amount of phosphorus getting into Lake Winnipeg has increased greatly over the past few decades due to the increase in the human population living in the watershed, the increase in the agricultural animal population, and the increase of application of fertilizers both in urban and rural settings. The drainage of almost 70 % of the wetlands in the Lake Winnipeg watershed has added to the problem as the wetlands used to filter and slow down water running off the land. As well the impacts of climate change are exacerbating the problem due to greater intensity in rain and snow storms which pull more nutrients off the land as run-off. The number of ice-free days on the lake is increasing and as it does, so does the growing season for algae. The average temperature of the lake water will be going up related to more ice-free days and that contributes to greater algal growth.
In 2013 the Manitoba government created the Lake Friendly Stewards Alliance whose goal is to co-ordinate efforts and promote leadership to reduce phosphorus and nitrogen loading and protect water quality. There are over 75 stakeholders who have signed the Lake Friendly Accord and pledged to be part of the solution. This is a very positive step but more concrete action is required to halt the deterioration in the health of Lake Winnipeg. This blog will explore ideas and experience from other jurisdictions that can contribute to faster action in restoring the health of Manitoba’s Great Lake.


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