By Pete Jopke, Water Resources Planner with the Dane County Land & Water Resources Department
Article first published in the 2022 Greater Madison Lake Guide, a Clean Lakes Alliance publication
Aquatic plant harvesting on the Yahara lakes
The Dane County Land & Water Resources Department manages an aquatic plant harvesting program with much of the harvesting occurring on lakes Mendota, Monona, Waubesa, and Kegonsa. Occasionally, other smaller waterbodies are harvested to aid in recreation and invasive plant management. The program dates to the early 1980’s when five harvesters were in operation. In those years, harvests totaled over 300 tons of plant material. In 2021, the existing fleet of 12 harvesters recorded plant harvests of more than 12,000 tons!
The importance of aquatic plants
Aquatic plants, which may include both desirable native plants along with invasive species, are an important part of any lake ecosystem. They provide oxygen, cover, food, shoreline stabilization, water quality improvements, and more. While the plants can become a nuisance at times, their advantages far outweigh the inconvenience and negative aspects that accompany them.
The Dane County Aquatic Plant Harvesting Program intends to provide relief when excessive plant growth interferes with recreational interests. Harvesters are not designed for, nor can they remove cyanobacteria (blue-green algae).
Aquatic plant growth
The Yahara chain of lakes is an incredibly complex system, and growth patterns of aquatic plants often change dramatically from one year to the next. During high-growth years, which many would say occurred in 2021, plant growth will always exceed harvesting, regardless of the number of harvesters or time spent cutting. We’ve also seen that improved water clarity conditions sometimes lead to more aquatic plant growth, which is a good reminder that aquatic plants do not always indicate a problem.
Over time, there have been tremendous changes within the watershed or land area that drains to the lakes. Our community creates runoff, which carries nutrients that help feed plants and algae. This isn’t necessarily a new problem as the area lakes were often treated with copper sulfate dating back to the 1920s as algae and plants created excessive water quality impairments.
A management plan
Harvesting follows permit requirements from the Wisconsin Department of Natural Resources (DNR). Each lake must have an approved Aquatic Plant Management Plan. Every five years, Dane County staff update plant management plans based on extensive field work along with public comments. Field work includes performing a point intercept survey or plant survey on all approved waterbodies, which involves sampling thousands of pre-determined locations where plants are identified and densities are recorded. The data are then entered into a spreadsheet that calculates many different metrics and helps guide any potential changes to the plans. All harvesting of aquatic vegetation occurs in DNR-approved locations. The areas typically avoid undeveloped shoreline areas or those with known hazards. Permits also restrict harvesting to waters deeper than three feet. This often means no cutting between piers as they may lie in shallower water.
Barge pickup program
An additional component to the program includes a barge pickup program. Dane County, in partnership with the City of Madison, Town of Westport, City of Monona, Lake Waubesa Conservation Association, and Friends of Lake Kegonsa Society, has a shoreline barge crew working to pick up aquatic trash and debris from residents’ piers from May through August. Barges service all of lakes Monona, Waubesa, and Kegonsa. On Lake Mendota, barges only cover the City of Madison and Westport locations.
The goals of the harvesting are to provide:
- Flood mitigation (keep water flowing through the Yahara River)
- Improved recreation, navigation, and beach access
- Shallow cuts for filamentous algae control
- Improved conditions for special events
The Dane County website shows dates and lake locations. Dane County staff will remove and dispose of lake material only. Lake material must be placed at the end of the pier.