Boats impact the littoral zone

Now that it's June, the true boating season has begun.  While you're out enjoying the lake this summer, there are a few concepts that will help you become a more informed boater and lake steward.

We'll start with a definition: the littoral zone.  The littoral zone is the area of the lake that is less than 15 feet deep and where sunlight can reach the bottom.  The littoral zone is usually where you will find the majority of aquatic plants since they need sunlight to grow.  The littoral zone is also important habitat for fish, shorebirds and aquatic invertebrates because the plants give them refuge from predators and there is abundant food available. 

Generally, the greater the percent littoral area, the more aquatic plants are in the lake.  We tend to think of aquatic plants as bad for recreation, but they are very important to organisms living in the lake.

The littoral zone and the plants and organisms living there are sensitive to boat use.  When a boat speeds through the littoral zone, the propeller can cause disturbance.  First, it stirs up the lake sediment, re-suspending nutrients (phosphorus) into the water.  These nutrients can then feed algae and cause and algal bloom.  This stirring can also decrease the water clarity because of additional particles suspended in the water column.  Secondly, props can cause direct damage to aquatic plants, cutting them up.  Thirdly, props and wave action can disturb sensitive habitat for spawning fish and other organisms. 

What you can do is make sure you drive slowly through littoral areas or avoid them entirely.  Imposing a speed limit doesn't always help because studies show that "near plane" speed, 6-8 mph, has maximum potential for stirring up lake sediments.

To determine where the littoral zone is in your lake, you can use the RMB Environmental Laboratories mapping tool: http://www.rmbel.info/Reports/Reports.aspx.  On the right-hand side, there is a legend that has different layers of map information.  Click in the lakes box, the bathymetry box and the littoral zone box.  You can search for your lake at the top of the page and it will zoom in.  You will then see your lake in blue, and the littoral zone in purple.

Until next week, enjoy the lakes!

Moriya Rufer is the Lakes Monitoring Program Coordinator for RMB Environmental Laboratories in Detroit Lakes, 218-846-1465, lakes.rmbel@eot.com.