Clear ice and aquatic plants

Have you noticed that the lake ice is extremely clear and smooth this year?  It has even been decent for ice skating on the lake.  This year the lakes froze over quickly before there was any snow, so the ice is very clear.

Clear ice without snow on top allows sunlight to shine through the ice and be used by algae and plants for photosynthesis.  This allows plants and algae to grow throughout the winter under the ice.  This can be both good and bad for the lake.  

It is good to have plants and algae growing under the ice, because when they photosynthesize they give off oxygen as a byproduct.  This oxygen is then available for fish, aquatic insects and other aquatic animals to breathe.  Since the ice cuts the lake off from the air in the winter, oxygen is harder to come by underwater unless plants and algae are producing it.  Lack of oxygen under the ice is what can cause fish kills over the winter.

When clear ice can be bad, is if you have Curly-leaf pondweed in your lake.  Curly-leaf pondweed is an aquatic invasive plant that is fairly wide-spread in Minnesota.  It is a nuisance because it can form dense mats in early spring that interfere with recreation.  When it dies off in early July, it washes up in thick piles on the shoreline.  Curly-leaf pondweed can grow through the winter if light is available, so if the ice is clear most of the winter, the Curly-leaf pondweed can get a good head start on growing and spreading. 

Some snow this past week has dusted the ground, so that has probably diminished the light shining through the ice.  We'll see what this winter has in store for us and for our lakes.

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