<p>WINNIPEG – A massive flood that has turned fertile Manitoba pastures into lakes and driven people from their homes for weeks on end will probably deal another blow to the ailing prairie ocean known as Lake Winnipeg.</p> <p>Flood waters that have settled across much of southern Manitoba are expected to carry various nutrients picked up from farmers’ fields and urban run-off when they do finally recede into the world’s 11th largest freshwater lake. It already has dangerously high levels of nitrogen and phosphorus, which feed huge blue-green algae blooms so large they are visible from space.</p> <p>Experts say this year’s flood, combined with a hot summer, could push nutrient levels up even more, as previous floods have done.</p> <p>”The more land you inundate, the more potential there is for nutrients to come in,” says Peter Leavitt, Canada research chair in environmental change and society, who recently conducted a study on Lake Winnipeg.</p> <p>”The forecast from Environment Canada is this will be a very hot summer – eventually. And if that’s true, you put a lot of light energy into the lake and you have the maximum potential to convert these dissolved nutrients into things that we don’t want to see, like silent bacteria blooms that float to the surface and drift on shore.”</p> <p>The blue-green algae can suck oxygen from the water and produce toxins that are harmful to fish, humans and other living things. With the rise of urbanization and intensified agricultural activity, Leavitt says algae in Lake Winnipeg has risen 500 per cent.</p> <p>”We see this progressive creep toward the future,” says Leavitt, a professor at the University of Regina. “It’s slow enough – just a few per cent per year – that you just don’t see it when you look at the lake from one year to the next. But when you look at it over a century, you see these large changes.”</p> <p>After the so-called flood of the century in 1997, phosphorus levels doubled in Red River water feeding into the lake. After another massive flood in 2009, levels were almost 40 per cent above normal.</p> <p>This year’s flood is dragging well into the summer and is covering a record swath of land. Thousands of people have been forced from their homes since the flood began in April, and the Canadian Wheat Board has estimated that between 2.4 million and 3.2 million hectares of farmland will go unseeded, mostly in Manitoba and Saskatchewan.</p> <p>Nicole Armstrong, director of the water science and management branch at Manitoba Water Stewardship, says the large volume of flood water this year does raise concern about increasing nutrients in the lake.</p> <p>”Just because there is more volume of water, there would be more nutrients going into the lake,” she says. “(Flood waters) also, of course, pick up nutrients as they pass over the land.”</p> <p>Armstrong said the impact of this year’s flood might not be obvious immediately. There are already enough nutrients in the lake to produce algae blooms in a good year, so Armstrong says beach-goers might not see a big change this summer.</p> <p>”We don’t always see a huge impact after a flood,” she says. “But certainly it brings more nutrients in that can continue to cause algae blooms over the long term.”</p> <p>The province is trying to nurse the lake back to health. The NDP government announced in 2003 that it wanted to protect Lake Winnipeg from being choked by pollution and toxic algae blooms. Since then, it has imposed controversial restrictions on hog farmers, banned the spreading of manure into the water and seriously curbed the use of pesticides near waterways. It has also banned dishwater detergents that contain phosphorus.</p> <p>The good news, Armstrong says, is that Lake Winnipeg is so large it doesn’t take long to clean itself – as long as it doesn’t continue to get bombarded by phosphorus and nitrogen.</p> <p>”The turnover time in the lake is actually quite quick,” she says. “It takes about four years on average for water to flush through the lake.”</p>
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