Operational Considerations for your lake.

Expected Results from a Weed Harvesting Program.

Most aquatic plant harvesting systems will cut and remove submersed plants to a depth of five or six feet. As this biomass is removed from the lake, the water is immediately ready for use and there are no restrictions on use of the area that might be experienced with herbicide or some biological control treatments.

Removal of this biomass prevents its eventual decay and settling to the bottom, helping to reduce sedimentation in the lake. There is some nutrient removal with harvesting too, as the nitrogen and phosphorous that is bound up in the plant exits the water body. Harvesting is usually not lethal, leaving behind an oxygen and possibly habitat producing plant, which may be desirable in some situations.

Many harvester managers have witnessed a reduction in nuisance plant growth after a few years of repeated harvesting. The plants showed signs of stress and came back thinner, lower growing, and more scattered than before. In some cases desirable plants were able to out compete the nuisance plant growth.

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For 40 years – 1945 to 1985 – the sanitary district used herbicides, including 2-4-D for 17 years, in an attempt to control the weeds. Since 1947, the district also harvested weeds from the lake and would pick up the weeds that washed on the shoreline.

In 1985, the use of chemical herbicides was discontinued on the lake and an expanded weed harvesting program began. The harvesting and removal of the plant material reduced nutrients available for the regrowth of the invasive watermilfoil and allowed for a better diversity of native aquatic plants.

The Lake Pewaukee Sanitary District understands the value the aquatic plants have on the stability of the lake bottom as well as value the plants have on the aquatic life thriving in the lake. They also understand the importance of keeping the aquatic plant levels down to allow human recreation.

The District starts its harvesting program earlier than any other lake in Wisconsin and runs the program longer than any other lake in Wisconsin in an effort to knock back the invasive species and promote the native species. The challenge becomes what the budget and time allows and the cost benefit of what is being accomplished. The District has been slowly increasing the equipment and labor force in an effort to continuously improve the harvesting operations. Small budget increases are helping increase manpower and more importantly set up the 2nd shift program for years that the cycle provides a peak aquatic plant growth season.

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