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Aquatic Vegetation Growth & Treatment

Why does the amount of vegetation in the waterways vary from year to year?


In some summers, many Wisconsin lakes have experienced an increase in aquatic vegetation growth. While there isn’t a quick or easy answer, water resource professional theorize that increases in aquatic vegetation are the result of a variety of occurrences:


  • Early and very warm springs boost the development of new plants.

  • Record breaking temperatures in the spring and summer with above average growing degree days.

  • More frequent and intense rain events increase nutrient loads to Shawano waterways and contribute to increased vegetation growth. Periods of calm winds, hot weather and an ample supply of nutrients throughout the summer can fuel the growth of algae and duckweed.

  • Zebra mussels in large numbers have the ability to make the water clearer because an adult zebra mussel can filter a liter of water per day, siphoning out all the small particles they encounter. Increased water clarity allows for more light penetration which aids the growth of aquatic plants.


In sum, clear water, nutrients, periods of calm weather, low currents, warm water and other factors all can affect vegetation growth in Shawano waterways.


Where is chemical weed treatment applied?


Each year SAWM does limited chemical treatment of nuisance weeds to enhance lake navigation and recreation. By DNR permit we are restricted to treating only the following areas:


  • The buoy lines on the north and south shores

  • The bay between the channel to the river and Webers Point

  • Cecil Bay area

  • Swan Acres

  • A section of the lake along Highway 22

  • A section of the lake more towards the middle of the lake


SAWM must apply for, pay for and receive DNR approval for the permit each year. The permit is based on the size of the area treated. The above areas are all specifically targeted because of high lake traffic and specific problems in those areas. All chemicals used are safe, biodegradable, DNR approved, and do no harm to fish or swimmers.


The channel and river are not sprayed primarily because the chemicals would be washed away by the current before they could become effective. In addition our DNR permit does not allow spraying in these areas.


SAWM is fortunate to have its own volunteer chemical applicator. Bart DeFere takes several courses on his own time and must pass a challenging testing program to be certified to make the chemical applications. We could not afford to do these treatments if we had to hire an outside company to do them. One of the SAWM barges has specifically been outfitted to do the spraying, including a special setup that includes tanks for chemical distribution.


What causes algae?


Algae blooms are an unusually dense growth of aquatic single celled plants. Excessive amounts of nutrients that enter our lakes leads to eutrophication (accelerated plant growth). Sometimes plant growth may be in the form of nuisance algae that “bloom,” turning the water pea green and sometimes even causing fish kills. They occur, frequently to the point where they discolor the water, when ideal factors combine to promote growth – generally light, temperature, salinity and nutrients. Algae blooms are a natural phenomenon but their frequency, duration, extent and density are all increased in waters where human activities on land increase nutrient runoff.


If your algae looks like fluffy clouds or cotton candy, there’s a good chance its filamentous algae, sometimes called “moss” or “pond scum.” Cladophora feels “cottony,” which spirogyra is bright green and very slimy to the touch, and pithophora (or “horse hair”) has a very coarse texture like horse hair or steel wool. As algae grow, it produces oxygen that gets trapped in the entangled strands of algae. This entrapped oxygen makes the algae buoyant and causes it to rise to the surface.


Algae are necessary for a healthy lake ecosystem, but there can be too much algae. When this happens, the grazers who eat the algae can’t keep up. As the uneaten algae die off, they sink to the lake bottom and decay. The process of decay requires bacteria, which in turn require oxygen. If there is an abundance of dead algae, bacteria use up too much oxygen, and there isn’t enough left over for all of the animals, like insects and fish. Too much algae can also give lakes an unpleasant green color or a surface scum.


Unlike toxic blue-green algae, which is blue-green in color (but can be brown or purple) and appears cloudy or like thick pea soup, Cladophora, pithophora and spirogyra are from the green algae family. Green algae don’t produce toxins but it is still important to think about practicing good hygiene, such as washing off, if you come in contact with it.


Short term, the best method for homeowners to remove filamentous algae is to rake out the floating clumps and compost these piles or use them in your garden as mulch. Chemical control requires a permit from the DNR. Long term, waterfront property owners and farmers can limit the amount of water and nutrients reaching the water. Reducing fertilizer use, keeping animal waste out of waterways and storm drains, preventing soil erosion on farms and construction sites, planting buffers along waterways, and keeping leaves and grass clippings out of the streets are just a few of the ways that we can all reduce phosphorous runoff over the long run to help keep the problems from getting worse.

Shoreline weeds:  Where do they come from?


You hurry up at the end of your week to get to the cottage.  You arrive to find floating plants at your shoreline.  You know how you will spend your Saturday morning.


So where do these weeds come from?  Here at SAWM we hear lots of comments that our weed cutting produces these floating weed masses which blow onto your shore.  Well, that is not the case.  We’ll explain.


SAWM picks up the weeds we cut.  Cut weeds are conveyored onto a barge and  offloaded and hauled to a landfill.

Shawano Lake if full of wild celery.  This plant uproots extremely easily during the summer.  It floats to the top and gets blown ashore.  This is a significant source of shoreline weeds.  But the good news is birds that occupy our lake, and migrate through, like wild celery.  This makes Shawano a preferred location for birds to live and migrate through, enhancing our lake experience.


Boat propellers chop up the salad of our lake weeds and it all blows to shore.


Natural death and decomposition of lake-based plant material contributes to shoreline weeds as well.


There may be additional reasons why weeds end up on your shore but we tried to identify the most significant.


So, we share the lake with our shoreline weeds.  But at least they can’t haul US to the dump!

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