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Imagine you're taking a walk along the beach on a beautiful summer's day.  If the beach in question is along the shores of Lake Winnipeg, the 10th-largest freshwater lake in the world, you could be in for a surprise.  Instead of sandy beaches you find a thick, green sludge reminiscent of pea soup.  Suppose your dog thirstily laps up the water and winds up dead an hour later (that's exactly what happened to one beach-goer's beloved pet in 2009).  What is happening to this once-pristine lake?  As biologist Al Kristofferson says, "We all assumed, somewhat naively, that nothing would happen to Lake Winnipeg.  Well, it did."

Lake Winnipeg has long been a beloved destination for vacationers and cottage owners. For generations, it has been a recreational hub for families, residents of Manitoba and tourists.  It is also home to an important fishery.  Those who have experienced and enjoyed Lake Winnipeg have a strong, personal connection to its vast beauty and depend on its productivity.  But we know very little about it. Save My Lake plunges into the science and environmental factors behind the slow death of spectacular Lake Winnipeg.  

The green sludge washing up on the shores of Lake Winnipeg is caused by high levels of chemical nutrients like phosphorous that have turned it into the most chlorophyll-polluted lake in the world.  The nutrients come from its huge watershed – a million square kilometers. Phosphorous provides nutrition for the growth of algae, which is a natural process in healthy lakes.  In the short term, excess algae have led to bumper fish catches and happy fishermen.  But when the algae die off, dead organic matter builds up and starts to decay, consuming dissolved oxygen.  The lake then chokes from the bottom up - a condition known as hypoxia.  The full extent of the blooms is only visible from space.

An overabundance of nutrients in the water now threatens not only the lake's beauty, but also the natural ecosystems underlying it.  Save My Lake reveals how a perfect storm of agricultural and hydro practices, sewage run-off, flooding and marsh destruction have affected the lake, and examines why Lake Winnipeg's ecology has changed so drastically in just three decades.  Among the reasons is one that may perhaps be surprising to some – hydro electricity generation.  Dams built and designed to keep water levels high may be good for moving turbines, but it also results in the flooding of nearby marshes.  As we discover, Netley Marsh plays a crucial role in the health of Lake Winnipeg, by breaking down the phosphorus and nitrogen-laden water that floods northward from literally tens of thousands of farmlands often situated over a thousand kilometres away.  Yet the marsh's vegetative size, once estimated at over 75 square kilometres, is now only 13.  Netley has been flooded away by Manitoba Hydro's use of Lake Winnipeg as an electricity-producing reservoir.

Of course, there is no one solution to reverse the unnatural growth of algae and its impacts, but by reducing the rate of nutrient flow off the land and restoring the lake's natural nutrient balance, Lake Winnipeg can stilll have a healthy and productive future.

Save My Lake is produced by Paul Kemp and directed by Jeff Newman for Stornoway Productions in association with CBC The Nature of Things.

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