Impacts of the Southern Lakes Concept on Waterfowl?

Energy Supply, Environment

May 12, 2016  Comment

Today's 'Ask Janet' question: Yukon Energy’s Southern Lakes Enhanced Storage Concept proposes to hold back the water 30cm higher in the fall, and drawdown the lake an additional 10 cm in the spring. Can you share what studies Yukon Energy has done to determine what impacts these proposed changes, particularly the additional 10 cm drawdown in spring, could have to migrating waterfowl habitat at M’Clintock and Swan Haven? Many people are concerned that a lower water level (even only 10cm) would dewater a large area of the shallow mudflats in spring, and may reduce the growth and availability of, or access to, aquatic plants – a critical food source to swans and other birds. Further, what impact would the increased fall water levels have on bird and frog habitat in the M'Clintock area? 

Thanks for the question. I'll break this down into two parts...first, your question about what effect drawing down Marsh Lake by an additional 10 centimetres in the spring could have on migrating birds at M'Clintock and Swan Haven. As I know you are aware, areas that become ice free in the early spring are very important to birds such as trumpeter swans and other migrating waterfowl. Later in the spring (early May onwards), there are more areas of open water and therefore the birds are often more widely dispersed.

If the Southern Lakes Enhanced Storage Concept were to move forward as a project, water levels throughout the month of April would be the same as they are now. We would gradually start using the additional 10 centimetres of storage in early May, with most of the water being used in late May. While this would probably result in more exposed mudflats than are seen currently, most of the migrating waterfowl, including the swans, will have already passed through the Southern Lakes area. The exposed mudflats could actually be a good thing for some of the later migrating species such as shorebirds, since they use this kind of habitat for feeding.

Now to the part of your question about holding back 30 centimetres of water in the fall...for this I need to talk about the remnants of the previous year's growth of aquatic plants. In the spring, many species of waterfowl feed on the roots of these remnants. The location and abundance of these plant remains depends on how deep the water is and how much light they received when they were alive and growing the previous year. With the concept in place, water levels during the time of year that these aquatic plants grow (June through August) would be the same as they are now. The gates at the Marsh Lake Control Structure would be fully open as per our water license and water levels would be determined by Mother Nature and not Yukon Energy. By the fall when the additional 30 centimetres of water begins to be used, the plant remains would be undergoing their natural, seasonal die off and so should not be affected by the concept.

I should make it clear that holding water levels higher in the fall would not involve flooding new ground. Many years, water levels already naturally exceed the elevation that we are proposing. Based on our research, we don't believe frogs or water birds will be adversely impacted by the Southern Lakes concept.

I know this was a long answer but I hope I have addressed your questions.


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