State of the Lakes Report

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2021 State of the Lakes Report

2021 State of the Lakes Report - Cover

Clean Lakes Alliance envisions a future in which everyone realizes the lakes are the center of our community. Surrounded by water, Greater Madison thrives because these stunning natural amenities make us special and different from anywhere else. The lakes are also constantly changing and impacted by the decisions we make. Like a living organism, the health of our waters reflects the quality of the surrounding environment that protects and nourishes them.

This annual State of the Lakes Report provides a window into how the lakes are doing each year. Additionally, it highlights the root causes of water quality challenges. It also casts a light on the status and effectiveness of cleanup efforts. We thank the many partners, scientific experts, and volunteer monitors whose contributions make these public reports possible. As stewardship action unfolds across a 485-square-mile watershed (Figure 1), knowing how the lakes are responding to ongoing change is the first step in charting a path toward their recovery.

Figure 1: Yahara Watershed showing land areas that drain directly to each lake. Yellow denotes agricultural areas that comprise most of the watershed.

Successes and setbacks

Conservation actions work. Thirty years of monitoring data from Lake Mendota’s stream tributaries show these actions lead to declines in sediment and phosphorus concentrations in streamflow entering the lakes. That means practices like cover crops, low-disturbance tillage, and following farmland nutrient management plans are doing their jobs. According to Dane County Land & Water Resources (2019), if climate variations were held constant, models show that the amount of phosphorus delivered to Lake Mendota would have decreased by 36% over the last two decades. Those findings speak to the effectiveness of conservation actions as they get adopted across the watershed.

James Madison Park Flood
James Madison Park on Lake Mendota, flooding in 2018

But a wetter climate and other factors are masking those impacts. Greater rainfall volumes and intensities combined with milder winters means more runoff and more algae-loving phosphorus entering the lakes. Today, all five Yahara lakes are classified as “impaired,” mostly because of excess phosphorus. There are also 13 beaches already listed (9) or proposed to be listed (4) as impaired due to problems with E. coli bacteria. The failure of our lakes and beaches to meet basic standards of quality and usability is seen in water resembling thick green paint. It is experienced with every beach closure warning of toxic cyanobacteria or E. coli contamination. And it is the smell in the air as thick matts of algae wash to shore and rot. Conservation actions may be working, but the lakes tell us much more is still needed.

Follow the water

The story of our lakes is written in the pathways of its water, beginning at the source. Data from the Dane County Regional Airport gauge show a total of 25.29 inches of precipitation fell across the watershed during the last “water year.” (Oct. 1, 2020 – Sep. 30, 2021). Compared to the normal of 34.48 inches, the significantly drier conditions interrupt a trend of above-average rainfall. The lakes typically respond favorably to drier weather. Drier weather contributes to less runoff, meaning fewer opportunities for pollutants to move from land to water.

Throughout the year, surface water steadily flows from north to south. This happens as it is funneled from the upper reaches of the watershed, through Yahara River stream tributaries, and down the chain of lakes before entering the Rock River. Monitoring data allow scientists to estimate the mass of phosphorus transported to the lakes over the year (called “loading”). Total loading can be highly variable. Long-term trends paint a picture that illustrates how climate and landscape interactions are impacting lake and stream quality.

A bellwether for the chain

Perched at the top of the chain and receiving most of the watershed’s drainage, the condition of Lake Mendota is a good indicator for how the downstream lakes will be impacted. Lake Mendota is also the largest lake with the greatest number of monitored streams and the most complete long-term dataset. The lion’s share of phosphorus received by the lower lakes is through the outlet of Lake Mendota as it gathers from the northern headwater regions of the watershed and cascades down the rest of the system.

Figure 2 shows the total pounds of phosphorus delivered from Lake Mendota’s monitored streams during the 2021 water year compared to prior years. During the 2021 water year, the 28,160 pounds of phosphorus loading to Lake Mendota was 48% below the long-term average (1990-2021).

Tributary Loads to Lake Mendota - 2021 SOTL - Figure 2
Figure 2: Phosphorus loads (in pounds) delivered to Lake Mendota through its monitored stream tributaries by water year. Also shown is total precipitation (in inches) during these time periods. Loading data source: T. Stuntebeck, USGS

Renew the Blue

Maintaining an annual average loading of 32,600 pounds is a Yahara CLEAN target recommendation. If attained, the number of days our lakes are clear and free of algal-blooms each summer should double. Yet an increasingly wetter climate makes reaching this target more challenging. Monitoring data show a widening gap between annual average loading and the desired target level. According to Renew the Blue: A Community Guide for Cleaner Lakes & Beaches in the Yahara Watershed (2022), a 57% reduction from current conditions is now needed to reach water quality goals (Table 1).

Average Annual P Loads - 2021 SOTL - Table 1
Table 1: Summary of average annual phosphorus (P) loads and targets (pounds/year) for the Yahara lakes. (1 – Lathrop & Carpenter, 2014. 2 – Sum of measured tributary loads plus estimates of ungauged areas (14%). 3 – 1976-2008 average multiplied by ratio of 1990- 2020 to 1976-2008 averages for Lake Mendota.) Table credit Renew the Blue: A Community Guide for Cleaner Lakes & Beaches in the Yahara Watershed

Figure 2 also shows total precipitation by water year and how it relates to loading. While yearly totals can be telling, it is the timing, intensity, and frequency of rainfall and snowmelt that ultimately offer the best predictors of runoff and phosphorus-loading conditions. For example, runoff events when the ground is frozen can have a disproportionately large impact regardless of yearly totals. This is evidenced by high ammonium concentrations in winter runoff samples. These findings link the land spreading of manure to high phosphorus loads observed during the January-March period (Figure 3). On average, phosphorus loading during that period accounts for 54% of the annual total.

Ammonium and Phosphorus Loads - 2021 SOTL - Figure 3
Figure 3: Ammonium runoff loads compared to phosphorus loads by season as measured between 2011-2020 from samples collected at the Yahara River at the Windsor stream gage. Loading data source and graphic: R. Lathrop, UW-Madison Center for Limnology

Screening for lake health

In-lake clarity and phosphorus data are collected by UW-Madison’s Center for Limnology as part of its Long-Term Ecological Research (LTER) program. Because of the COVID-19 pandemic and its impacts on personnel availability, center- of-lake summer phosphorus concentrations were not obtained for lakes Monona, Wingra, Waubesa, and Kegonsa in 2020, and lakes Waubesa and Kegonsa in 2021.

Figure 4 shows summer median total phosphorus concentrations for 2021 compared to recent years. For deeper lakes Mendota and Monona, phosphorus levels are considered “fair” by Wisconsin Department of Natural Resources standards. For shallower Lake Wingra, conditions are considered “good.”
No LTER phosphorus data were available for the lower lakes, Waubesa and Kegonsa.

P Trends - 2021 SOTL - Figure 4
Figure 4: Median summer phosphorus concentrations (in mg/L) and corresponding water quality conditions as defined by Wisconsin Department of Natural Resources standards. Data source: R. Lathrop, UW-Madison Center for Limnology

Figure 5 shows summer median water clarity readings for 2021 compared to recent years. Values represent the depth to which a transparency-measuring device, called a Secchi disk, can be seen when lowered from the water surface. Clarity readings hover between “good” and “fair” conditions for lakes Mendota, Monona, and Wingra. The much smaller and shallower Lake Wingra continues to exhibit water quality benefits from carp removal in 2008. Carp are known to stir up lake bottoms through their feeding behavior. For Lake Waubesa, conditions are considered “fair,” while Lake Kegonsa experienced an “excellent” year for water clarity.

Clarity Trends - 2021 SOTL - Figure 5
Figure 5: Median summer water clarity readings (in feet of transparency as measured by a Secchi disk) and corresponding water quality conditions as defined by Wisconsin Department of Natural Resources standards. Data source: R. Lathrop, UW-Madison Center for Limnology

The lake user experience

Ultimately, we want our lakes to be safe and swimmable. They should be free of the cyanobacteria blooms and E. coli contamination that can close beaches and pose public-health risks. Thanks to the dedication of Clean Lakes Alliance’s all-volunteer monitoring network, a record 85 reporting stations were active across all five lakes during the 2021 season (Figure 6). Trained monitors contributed 2,105 LakeForecast condition reports from approximately Memorial Day to Labor Day.

LakeForecast Monitoring Sites - 2021 SOTL - Figure 6
Figure 6: 2021 LakeForecast monitoring sites

The number of days when one or more monitors reported “strong evidence” of a cyanobacteria bloom is summarized for each lake in Figure 7. By comparing the number of ‘algal days’ to the total number of unique sampling days for each lake, a percentage can be generated that better represents the number of blooms witnessed each year. This method eliminates overreporting in situations when different monitors report the same algal bloom.

Days with Report of Cyanobacteria - 2021 SOTL - Figure 7
Figure 7: LakeForecast nearshore monitors reporting “strong evidence” of a cyanobacteria bloom represented as a percentage of total sampling days

Compared to the prior year, 2021 saw more “strong evidence” of cyanobacteria blooms on the four primary lakes, with Monona and Waubesa at their highest reported levels compared to the last six years. Lake Wingra remained consistent with no reports of strong cyanobacteria blooms.

There was significant variability in algal days across each lake. Generally, the highest number of strong cyanobacteria blooms are reported in June and July, followed by a sharp decline in August. May and September often have fewer strong reports of cyanobacteria. This is because fewer monitors are active, and the typically cooler weather does not support the rapid algal growth seen during warmer months.

Water quality trends

Clarity reports did not reveal any consistent trends across the five lakes when compared to 2020. Lake Kegonsa and Lake Wingra demonstrated an improvement in water clarity, while Mendota, Monona, and Waubesa saw moderate reductions when compared to the previous year. These observations also hold true when compared to the long-term median water clarity measurement for each lake. Except for Lake Wingra, overall water clarity in 2021 for the Yahara lakes was relatively poor when compared to previous years.

As depicted in Figure 8, average clarity for most lakes decreased throughout the summer with a peak decline in August. Lake Kegonsa deviated from this trend as clarity readings were at a season low in September. The shallower depths of Lake Kegonsa, combined with its low-elevation position within the watershed and chain of lakes, likely contributed to the lower clarity readings.

Average Nearshore Clarity - 2021 SOTL - Figure 8
Figure 8: Change in average nearshore water clarity by lake during the 2021 season. Measured in centimeters of transparency using a 120-centimeter turbidity tube; murky is 0-50 cm, fair is 50-80 cm, and good is 80-120 cm of transparency.

Observations from the 2021 monitoring season demonstrate the difficulty in identifying whole lake trends in water clarity and algal presence. Despite an unusually dry year, water quality conditions were generally poor when compared to historical LakeForecast data. The data highlights the fact that the complex interactions of multiple variables affect water quality. There can also be long lag times between watershed actions that reduce phosphorus and lake response. The data collected by LakeForecast volunteers offer a valuable tool to help us better understand cause-and-effect relationships as they apply to ever- changing lake conditions.

Beach closures

As for beach closures, there were 267 total “closure days” documented during the 2021 summer-recreation season (Figure 9). Closure days represent the number of days each monitored beach had to be closed due to unsafe water conditions. These unsafe conditions are most often due to the presence of elevated and potentially harmful levels of E. coli and/or toxin- producing cyanobacteria. For historical comparison, the long-term median closure rate (2005-2021) is 107 days lost per season.

Beach Closure Days - 2021 SOTL - Figure 9
Figure 9: Beach closure days by lake from 2013-2021. Data source: Public Health Madison & Dane County

Emerging concerns

Clean Lakes Alliance has long focused on building capacity and partnerships around phosphorus reduction, seeking to apply maximum pressure to what is arguably the lakes’ single largest driver of water quality problems. This laser focus allows us to direct the public’s attention to where it is most needed, and has produced many notable wins, including leading the Yahara CLEAN Compact’s work in producing a Renew the Blue stakeholder guide to cleaning up our lakes and beaches. A community unveiling and official launch of the Renew the Blue initiative begins in May of 2022 as part of a culminating public event.

However, many other factors affect water quality conditions. They include over-salting during the winter months, the introduction and spread of aquatic invasive species like zebra mussels, and contamination by largely unregulated PFAS/PFOS “forever chemicals” that threaten human health (Figure 10) – to name a few. Clean Lakes Alliance will continue to raise awareness about these concerns while either leading or supporting actions that confront these challenges head on. That includes advocating for needed policies and bringing “Clean Boats, Clean Waters” watercraft inspectors to several busy boat landings in partnership with Dane County and the Wisconsin Department of Natural Resources.

Fish Consumption Advisory - 2021 SOTL - Figure 10
Figure 10: Fish-consumption advisories due to elevated levels of PFAS and PFOS. Credit: Wisconsin Department of Natural Resources

Looking ahead

Starting with the next State of the Lakes Report, readers will be introduced to a new progress-reporting dashboard. The new dashboard will follow guidance set forth in Renew the Blue: A Community Guide for Cleaner Lakes & Beaches in the Yahara Watershed. This will offer a more accurate and comprehensive representation of our collective progress. As in past reports, the focus will be on celebrating successful partner efforts and to maintain transparency and accountability as our work together proceeds.

About the State of the Lakes Report

The State of the Lakes Annual Report is released each year as part of the Greater Madison Lake Guide. In it, we report out to the community on the state of water quality in our lakes. The report also looks at our collective progress toward our phosphorus reduction goal.

The report highlights information from many partners to share the most up-to-date science on water quality in our lakes. We feature local projects, including work in urban areas to protect stormwater quality and progress on farms to keep nutrients on the fields and out of our lakes.

In addition, we provide more information about Clean Lakes Alliance and our efforts to engage the community and advocate for the lakes. This report serves as a reference and a resource, highlighting community progress toward cleaner, healthier lakes for all.

Learn more about our lakes

Learn more about lakes Mendota, Monona, Wingra, Waubesa, and Kegonsa.

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