Learning to love shallow lakes

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Posted by Angie Hong | Posted in Aquatic Biology | Posted on 16-07-2010

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Do you know the Rolling Stones song, “You can’t always get what you want?” I have a tendency to hear it playing in my head when I’m talking to people about shallow lakes. You see, shallow lakes suffer from a perception problem. Much like the person who buys an economy car and then “pimps it out” with revolving rims, tinted windows and a giant stereo system, people who live near shallow lakes tend to expect their lake to be something it’s not.

 By using the DNR lake finder tool, one can easily access information about local lakes, including their size and depth, water quality and fish species they support. One characteristic the lake finder data includes is the littoral area of a lake. This is the total area of a lake that is less than 15 feet deep, where the majority of aquatic plants and animals can be found. Perusing the data, one learns that White Bear Lake is 83ft deep at its deepest point and that nearly half of the lake is more than 15 feet deep. Forest Lake, on the other hand, is roughly equivalent in size but only 37 feet deep at its deepest. In addition, about two-thirds of Forest Lake is less than 15 feet deep. Many of the smaller lakes in the east metro area are quite shallow. Lake Olson in Lake Elmo is only 15 ft deep, while Lake McKusick in Stillwater is just 12.5 feet deep and Colby Lake in Woodbury is a mere 11 feet deep.

Shallow lakes are neither better nor worse than deep lakes, but they are definitely different. For one thing, shallow lakes tend to have much more aquatic vegetation, making them the perfect habitat for a wide variety of wildlife and waterfowl. Because they lack deep, cool waters, however, they are unable to support large fish like walleye and northern pike. The effects of eutrophication from runoff pollution can often be seen more easily in shallow lakes, where there is less water to dilute the excess nutrients. As a result, many shallow lakes in urban areas turn green quite early in the summer.

The key to loving shallow lakes is to understand that they essentially exist in one of two states: clear with vegetation or turbid without vegetation. Aquatic plants such as bulrushes, cattails, coontail, lilies and even some forms of algae provide important food and habitat for fish and smaller aquatic animals as well as absorbing phosphorus and other nutrients in the water. When these plants are removed, invasive species such as Eurasian watermilfoil and curly-leaf pondweed often take their place and blue-green algae can bloom out of control.

This summer, for example, many people have noticed that the filamentous algae, which creates floating massed on local lakes, seems more plentiful than usual. This is not necessarily an indication of poor water quality, however. Staff from the Ramsey-Washington Metro Watershed District investigated reports of excess filamentous algae on Spoon and Keller Lakes in Maplewood and discovered that although the algae was spreading on top of the water, the water clarity was excellent. They were able to see secchi disks lowered all the way to the bottoms of the lakes (2 meters on Spoon Lake and 1.7 meters on Keller Lake), which means very little blue-green algae and lots of dissolved oxygen for fish in the water.

Many of our frustrations with shallow lakes in our communities would be eliminated if we learned to love them for what they are – excellent wildlife habitat, essential links in the watershed chain, which help to absorb pollutants and excess nutrients as well as limit flooding, and beautiful scenery in our backyards and along our trail corridors. They’ll never be the crystal-clear and sandy-bottomed lakes we visit up north, and they might not be the best for waterskiing and swimming, but then again, that’s a little like expecting a Honda Civic to be a Corvette.

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