Q. I am wondering why the lakes are much more weedy than a few years ago.
Could it be from fertilizer? I fish Maple and Union lakes in Minnesota. They seem
to be getting worse every year.
A. There could be several reasons for what you're observing.
The first question that comes to mind is whether the "weeds" you mention are aquatic vegetation or algae blooms.
In the case of algae blooms, a Google search led me to the Indiana University Center for Earth and Environmental Science website. According to the website, runoff and soil erosion from fertilized farmlands and lawns and sewage effluent are major sources of phosphorus and nitrogen entering the water, which in turn promote algae growth.
Lakes with an abundance of cabins-and well-groomed lawns-certainly are susceptible to such conditions. The result can be water that looks like pea soup or those slimy floating blobs of green nastiness that begin showing up in shallow bays of many lakes this time of year.
My guess is that is what you're seeing in the two lakes.
In the case of Union Lake, the weeds you're seeing could be Eurasian watermilfoil, an invasive species documented in the Polk County lake in 2007. As a result, Union Lake is listed as an infested water for the invasive plant, which forms thick mats on the surface of the water and a tangled web of stems farther down.
According to the Minnesota Department of Natural Resources, Eurasian watermilfoil "can interfere with water recreation such as boating, fishing and swimming. The plant's floating canopy can also crowd out important native water plants."
Minnesota and North Dakota both have laws requiring boaters and other water recreationists to remove plant material from boat trailers and other equipment before transport in an effort to prevent the spread of Eurasian watermilfoil and other undesirable species.
Maple Lake isn't listed as an infested water for Eurasian watermilfoil or any other invasive species.
The other consideration, of course, is that the weeds you're seeing are native vegetation, which is a good thing if that's the case. Native aquatic vegetation benefits a variety of fish and aquatic animals, and removing it from a lake or stream can have a negative impact, including opening the door for undesirables such as Eurasian watermilfoil to gain a foothold and spread.