Large lake plants (called macrophytes) are an essential part of healthy lake and stream ecosystems. They are home to many aquatic animals and provide cover for young fish avoiding predators. Large lake plants also stabilize bottom sediments and reduce shoreline erosion.
Some rooted aquatic plants are weedy, especially exotic (non-native) plants, such as Eurasian water milfoil that first arrived in area lakes in the 1960s. Excessive growth of Eurasian water milfoil makes it the most abundant rooted plant in the Dane County lakes.
This canopy-forming growth characteristic is what makes Eurasian water milfoil such a nuisance to us. In particular, dense growth of the exotic plant interferes with boating and swimming, and the plants may produce an unpleasant odor when they die during summer. Eurasian water milfoil is usually the plant that lakeshore property owners, boaters and swimmers complain about, and with good reason. This weed (a "weed" is merely a plant out of place -- it is growing in the wrong spot) degrades the enjoyment and the ecology of the lakes.
As with many problem exotic species, we are unable to eliminate Eurasian water milfoil from Dane County lakes. The plant continues to flourish in our lakes because the bottom sediments are a repository of excessive loads of nutrients from urban and rural runoff over the last 150 years. The goal for the most effective management is to mechanically harvest the plants where they are at nuisance levels and take the cuttings for composting in gardens.
Dane County Nuisance Plant Harvesting Program
The Dane County Land and Water Resources Department through its Parks Division manages an Aquatic Plant Harvesting Program for county waters, with support from the Dane County Office of Lakes and Watersheds. Harvesting follows permit requirements from the Wisconsin Department of Natural Resources and approved Aquatic Plant Management Plans for each waterbody. The Dane County Lakes and Watershed Commission, Dane County Parks Commission, and elected county officials provide oversight.
Dane County currently has a total of ten mechanical harvesters and assorted other harvesting equipment. The county hires seasonal limited term employees to perform the harvesting. The supervised crews harvest aquatic plants from mid-May until mid-August. Crews are trained to focus on areas with exotic plants and to avoid areas with more native aquatic plants.
Adhering to DNR requirements and operating within the county's limited budget, the county's policy is to cut and harvest Eurasian water milfoil and other invasives to help provide for reasonable use of the lakes for boating, fishing and swimming, while preserving the health and balance of the lake ecosystem. Harvested plants are hauled by truck to remote compost sites.
Maps of the harvesting sites are found here:
There are aquatic management plans for each of the five lakes:
There are four priorities when cutting weeds on the lakes.
Priority #1 – Maintaining Consistent Water-Flow through the Yahara River
This priority is assigned only to the Lower Yahara River between Lakes Waubesa and Kegonsa, and is done to maintain water-flow and mitigate high water issues including potential flood conditions. Cutting is confined to the deepest part of the river channel in order to maximize water flow downstream. The section just north of Dyreson Road is rarely cut due to machinery hazards.
Priority #2 - Recreation and Navigational Access
This is the type of cutting traditionally provided by County harvesters: a 30 foot swath cut parallel to shore with periodic 20 foot access lanes cut to open water, to provide for recreation and lake access. These cuts are typically 4-5 feet deep. The cutting lanes are parallel to shore at a distance of 100-150 feet. This category includes cutting done to provide access from private shorelines, public Lake Access Sites (boat landings), swimming beaches and developed public shorelines.
Priority #3 –Shallow Cut: Over exposed Eurasian Water Milfoil Plant Beds and the collection of Filamentous Algae
Beginning in 2006, the DNR approved a program on the Yahara Chain of Lakes allowing for shallow cuts (2-3 feet deep from the surface) targeting Eurasian water milfoil in order to provide better access for recreational activity. A side benefit of these shallow cuts may be reducing filamentous algae mats, which form and frequently sit on top of the Eurasian water milfoil. DNR is satisfied that the shallow cutting will not harm fish habitat, leaving the anchored vegetation in place as habitat.
Priority #4 – Special Events
As time and budget permits, harvesters cut plants for special events held on or in the water. Only the minimal amount necessary for the event is cut. These are not mapped because locations vary; however, two examples are the mooring area for sailboat regattas held offshore from Bishop's Bay Country Club on Lake Mendota, and the "Ironman" swim course near Monona Terrace.
Areas Not Identified on the map – Harvesting is not prohibited in these areas; they are typically not harvested due to very minimal nuisance plant growth and budget limitations.
To locate where County harvesters are currently working or to view maps (Yahara Chain of Lakes) that provide a general guide of the locations where harvesting can occur please view the Harvesting Map links listed above. Please note that the width of the priority harvesting bands indicated on the maps was chosen to be visible at various map scales, and does not indicate the exact extent of areas that will be harvested.
No-Cut Areas – Native Plants
These areas have significant populations of beneficial native plants that Dane County, working with the Department of Natural Resources, intends to protect and encourage. These areas are not all identified on the map, as they may change from year to year. Additional areas will be added as they are identified by DNR aquatic plant staff, and will be protected as much as possible. Example: University Bay of Lake Mendota.
No-Cut Areas – Machinery Hazard
These are rocky or shallow areas where the harvesting equipment cannot operate due to potential damage to the equipment. Example: southwest corner of Lake Waubesa.
No-Cut Areas – Undeveloped Shoreline
These are undeveloped areas where access for motorized navigation is not needed. Example: north shore of Lake Kegonsa between the Yahara River mouth and Door Creek.
No-Cut Areas – Fish habitat
These are important fish spawning and juvenile fish cover areas located outside of the typical harvesting lanes, where harvesting would reduce fish production. Example: offshore from Hudson Park on Lake Monona.