State of the Lakes Report
The Yahara River Watershed encompasses lakes Mendota, Monona, Wingra, Waubesa, and Kegonsa, and is home to a fast-growing population and some of the most productive farmland in the United States. The intersection of productive farms and growing urban areas presents unique challenges as we work to improve water quality.
Lake water quality is a reflection of the health of the landscape. Many of the decisions we make on the land impact the health of our lakes, from how we manage manure, to how much winter salt we use.
At Clean Lakes Alliance, we focus on curbing the biggest culprit of our water quality problems—phosphorus runoff that results in the excessive growth of potentially toxic cyanobacteria (also known as blue-green algae). Phosphorus that makes its way into our surface waters is found in leaves, soil, and animal waste. It is found at higher than natural levels in our lakes because of how we use and manage surrounding lands. The trend toward more frequent and intense rainstorms and winter snowmelt only exacerbates the situation by generating more runoff that carries phosphorus to our lakes. The total amount of phosphorus entering the lakes is called “loading.”
This State of the Lakes Report shows the impact of phosphorus on lake water quality and beach closures in 2019. Each lake has a unique story, but overall, it was another challenging year for our lakes. Water clarity ranked “good” and phosphorus levels ranked “fair” for most of the lakes, according to Wisconsin Department of Natural Resources (DNR) criteria, and there were a comparatively large number of beach closures.
These conditions can be tied in part to wetter than normal weather. Large runoff events, especially in the late winter when the ground was frozen, contributed to the highest annual phosphorus loading since the 1990s.
Overall, phosphorus loading was 40% higher than 2018 when we had massive flooding. 2019 also saw 146 days of beach closures, or 39 more closure days than the long-term median (2010-2019). Cyanobacteria blooms were the primary cause of the 2019 beach closures, and were likely made worse by invasive zebra mussels. Zebra mussels consume free-floating algae and zooplankton, but they leave cyanobacteria—which compete for the same nutrients and sunlight—largely untouched.
If land management surrounding our waters does not change to accommodate an increasingly wet climate with more extreme rain events, our lakes are likely to continue to experience poor water quality. These challenges are why Clean Lakes Alliance is advocating for and investing in individual and community actions through the Yahara CLEAN (Capital Lakes Environmental Assessment and Needs) Compact. This coalition of government, nonprofit, and industry association leaders is working together to update lake-improvement recommendations and accelerate the adoption of effective solutions. We also worked with partners to develop an at-home actions guide for improving the watershed, raised money to support conservation practices on farmland, and promoted leaf-free streets (the largest source of urban phosphorus pollution).
About the watershed
- The Yahara River Watershed begins in the headwaters of the Yahara River in Columbia County, and encompasses lakes Mendota, Monona, Wingra, Waubesa, and Kegonsa throughout Dane County. The Yahara River then empties into the Rock River in Rock County.
- Invasive species like zebra mussels and the spiny water flea are impacting the food web in the lakes, creating conditions that favor cyanobacteria blooms during hot, calm conditions.
- Conservation practices and manure management on farmland and green infrastructure in urban areas (like rain gardens) help make our watershed more resilient while keeping phosphorus out of the lakes.
What happened in 2019?
Record levels of phosphorus flow into Lake Mendota
- 2019 was the 5th wettest year on record in the region, with greater than normal total precipitation and heavy rain events recorded at the Dane County Regional Airport. All the lakes were above their summer maximum water levels for a majority of the summer (May 1 – October 30).
- Rivers and streams flowing into Lake Mendota carried phosphorus into the lake in record amounts, the highest levels since intensive monitoring began in the late 1980s, and more than double the long-term average (see figure below).
- The majority of phosphorus loading to the lakes occurred during an unusually large snowmelt period in March.
Conservation practices are making a difference
- Separating out the effect of streamflow on water quality allows us to see the impact of watershed management, such as the adoption of conservation practices by landowners, over the past 30 years.
- According to an analysis by Matt Diebel of Dane County Land & Water Resources Department, if weather-related streamflow had not increased and did not vary from year to year, estimated phosphorus inputs to Lake Mendota would have decreased by 36% during the period 1990-2019, suggesting conservation practices would have been effective in an unchanging climate.
What impacts water quality?
- Phosphorus, a nutrient found in soil, manure, leaves, » and organic matter, enters the lakes in runoff and fuels algal blooms. The amount delivered into the lakes can vary greatly from year to year due to variations in land use and runoff-producing weather events. Reducing phosphorus in the upper lakes (Mendota, Monona, and Wingra) is essential to reducing it in the lower lakes (Waubesa and Kegonsa) as phosphorus flows downstream and accumulates.
- Late winter runoff events, when rain falls on frozen ground and cannot infiltrate into the ground, are when most of the annual phosphorus load reaches our lakes.
- Fall precipitation creates a phosphorus-rich “tea” when leaves are left to decay in the street. Because Madison storm sewers lead directly to the lakes, leaves represent the biggest source of phosphorus from urban areas.
- Invasive species, like zebra mussels, are changing the lake ecology and creating conditions that can worsen water quality.
- A changing climate, projected to be warmer and wetter in southern Wisconsin, is working against efforts to improve water quality.
Although it seems there are many forces negatively impacting water quality, it is important to remember that the actions we take on the land can help improve it. Read about ways to help the lakes from your home.
Water residence times and lake stratification
The figure below shows the water residence time of each lake, which is the length of time it would take to completely “flush” its entire volume of water. Deeper surface waters like Mendota and Monona thermally stratify in the summer, meaning a warmer water layer lies on top of a substantially colder water layer. This leads to a reduction in the amount of nutrient-rich water at the bottom that mixes to the surface where it can fuel cyanobacteria growth. Stratified lakes tend to have better summer water quality compared to shallower, mixed lakes like Wingra, Waubesa, and Kegonsa.
Water quality goals
Once Yahara CLEAN phosphorus-reduction goals are realized, University of Wisconsin scientists have estimated that we will double the number of summer days when the lakes are clear and free of cyanobacteria blooms.
We experienced 146 beach-closure days in 2019 due to cyanobacteria and high E. coli levels from Memorial Day to Labor Day.
To put this into context, each beach offers 99 possible beach days from Memorial Day to Labor Day. Multiplying this by the number of beaches we include in this report, 17, we should have 1,683 total beach days per year.
What causes beach closures?
- Invasive aquatic organisms, like zebra mussels and spiny water fleas, alter native food webs and phosphorus availability, creating conditions that lead to cyanobacteria blooms, floating algal mats, and beach closures.
- High E. coli bacteria levels at beaches can occur for several reasons. Commonly, rainstorms wash dog or bird feces into our lakes, allowing pathogens to enter our waters from nearby stormwater outfalls. Bacterial contamination can also come from manure runoff.
- Cyanobacteria, also known as “blue-green algae,” is an aquatic photosynthetic form of bacteria that can take on different colors and appear as a paint-like scum on the water surface. Abundant phosphorus combined with hot, calm weather creates ideal cyanobacteria bloom-forming conditions. Wind can then push floating scums to downwind shorelines where it accumulates and rots, producing noxious odors. Public health officials close beaches when blooms are present because they are potentially toxic and can lead to various health concerns. Toxins can also poison fish and other water-dependent wildlife, and rob the lake of life-sustaining dissolved oxygen.
Phosphorus reduction – an update on our community’s progress
See our 2019 lake by lake reports – find out how the water was in each of our lakes!
About the State of the Lakes Annual Report
The State of the Lakes Annual Report is presented each year at the Clean Lakes Alliance Community Breakfast. In it, we report out to the community on the state of water quality in our lakes and 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.
- 2018 State of the Lakes Annual Report
- 2018 Progress and Challenges video – shown at the 2019 Community Breakfast “Join the Wave”
- 2017 State of the Lakes Annual Report
- 2016 State of the Lakes Annual Report
- 2015 State of the Lakes Annual Report
- 2014 State of the Lakes Annual Report
- 2013 State of the Lakes Annual Report
- 2012 Annual Report / 2012 State of the Lakes Report
- 2011 State of the Lakes Report