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Aquatic plant transport barge on Lake Mendota

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!

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Water quality monitoring equipment

LakeForecast water quality monitoring in 2021

In 2021, our volunteers embarked on the 9th season of LakeForecast water quality monitoring. This work involved collecting nearshore condition reports at piers, beaches, parks, and access points around the five Yahara lakes. From May through September, volunteers took water quality measurements. They measured water clarity, recorded air and water temperature, identified the presence of green algae and cyanobacteria, and noted additional visual observations. Reports are entered into the LakeForecast app where all data are updated in real time.

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Filamentous Algae (Courtesy Joe Campshure and Terri Lefebvre)

Beautiful sunsets, majestic sailboats, and shoreline views of the Wisconsin State Capitol are some of the more familiar and picturesque sights around the Yahara lakes. But what else can we see across these thriving and complex ecosystems? On your next walk around the lakes, keep your eyes peeled and you may spot a fascinating lake phenomenon.

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Cyanobacteria on Lake Mendota at the Memorial Union

Cyanobacteria

All five Yahara lakes saw cyanobacteria (blue-green algae) blooms throughout the summer of 2019. One bloom in particular on Lake Mendota was quite large, covering at least an area from Picnic Point to the Memorial Union on August 1st. The bloom was well-documented by photos from community members as having a green pea soup-like consistency.

Cyanobacteria blooms are often bright green, but can also appear in shades of brown, blue, and white. Typically, blooms are spotted on warm days with calm winds. On August 1st, Madison reported a high of 81 degrees with an average wind speed of two miles per hour. 

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2018 Flooding

Yahara Lakes 2018 Water Quality Monitoring Results

Overview

From May to September of 2018, water quality monitoring took place at piers and beaches around the five Yahara lakes. Volunteers measured near-shore water clarity, air and water temperature, and noted several visual observations. Visual observations included presence of algal blooms (green/blue-green), floating plant debris, swimmers, waterfowl, wave intensity, and general water appearance. Volunteers report conditions on our website, Lakeforecast.org. The website displays updated data in real time.

Highlights

  • 79 near-shore and 7 offshore monitoring stations on all five Yahara lakes (Figure 1)
  • Weekly off-shore measurement of Secchi depth on all five lakes
  • Measured temperature and dissolved oxygen profiles on all five lakes (seven sites total)
  • Weekly monitoring continued at all 25 public beaches
  • 44% increase in number of condition reports from 2017 (Table 1)
  • Collected continuous near-shore temperature measurements at 17 sites on lakes Mendota, Monona, and Waubesa, and Kegonsa
  • Implemented E. coli sampling and cyanobacteria toxin testing pilots
  • Averaged 2.3 condition reports per site each week across all sites
  • Continued weekly Weekend Lake Reports with over 77,000 views on social media
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Water Quality Monitoring

2017 monitoring season

What started in 2013 as a handful of Clean Lakes Alliance board members testing the water has now grown into a network of over 70 volunteers doing weekly water quality monitoring on all five lakes.

Each week this summer, our team of monitors gathered data on water clarity and temperature. They also made visual observations on beach conditions and identified potentially harmful cyanobacteria (blue-green algae) blooms. And what a summer it was!

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