Environmental History of Eagle Lake
Welcome to CHAPTER 1 of our educational series,
“Ten Things You Should Know About Eagle Lake’s Environmental Challenges."
 
“You can’t go back and change the beginning, 
but you can start where you are 
and change the ending.”    C.S. Lewis
 
Eagle Lake is a shallow drainage lake located in the Town of Dover, Racine County, Wisconsin.  The lake is an important resource within the Illinois-Fox River Basin.  It provides a variety of recreational opportunities for the local community and the region, including boating, swimming and fishing.
 
To best understand Eagle Lake's environmental challenges, we need to take you back in time over 10,000 years!
Click on the highlighted sections below
to explore the details of each topic and continue through the entire webpage to expand your knowledge of our lake.
This is a lengthy chapter, but well worth the time you'll spend here.

Glaciers in Wisconsin - 10,000 Years Ago

In Wisconsin, we owe much of our modern hydrologic landscape of wetlands, ponds, lakes, streams, and rivers to the last ice age, when a vast ice sheet reshaped the land, left behind thick glacial deposits, and ultimately reorganized surface and groundwater systems.

The last major ice age in North America—the Wisconsin Glaciation—is named after our state. The Laurentide Ice Sheet was the larger of two ice sheets that covered most of Canada and, along its southern margin, flowing through the Great Lakes basins into the Midwest. The glacier’s behavior was complex, but in general, ice covered large parts of northern and eastern Wisconsin starting about 30,000 years ago and finally melted out of the state about 10,000 years ago.

Farming Wheat and Corn in the mid-1800's

The first farmers who came to Wisconsin were primarily from upstate New York, arriving between 1838 and 1850.  These early settlers initially focused on growing wheat, which became the staple crop for most Wisconsin farmers until the late 19th century.  The southeastern part of Wisconsin was among the first areas to be settled and farmed.  By 1849, there were already 117 mills in the state to process the wheat being grown.  However, by the late 1850s, wheat prices began to drop as yields diminished, leading to a gradual shift away from wheat farming, particularly in southeastern region.  Wisconsin eventually became a leading producer of sweet corn and silage corn.  The shift from wheat to dairy farming in southeastern Wisconsin had several significant effects on the region's demographics.

Watershed - The Importance of 4,228 Acres

A major source of water to Eagle Lake comes from rainfall, stormwater runoff, and snowmelt flowing from the 4,228-acre drainage area located entirely in the Town of Dover.  The total watershed area-to-lake ratio is 8:1. This is a high watershed area-to-lake ratio that suggests land use within the watershed tributary area to Eagle Lake has a direct impact on lake water quality.

Approximately 1,900 acres of the watershed are used to produce corn, soybeans, hay or other cash crops.  The Racine County Land Conservation Division model revealed 220 tons of sediment and approximately 475 pounds of phosphorus are delivered to Eagle Lake annually.  The estimated annual sediment load from existing urban land uses in the Eagle Lake watershed is 68 tons per year and the estimated phosphorus load is 178 pounds per year.  Active streambank erosion was identified as a significant contributor to the sediment load.  An estimated 2,900 feet of streambank are actively eroding in the lake watershed generating approximately 28 tons of sediment and 150 pounds of phosphorus.
 
Approximately 144 feet of lakeshore is actively eroding and generating approximately 10 tons of sediment and 80 pounds of phosphorus per year.  The total annual sediment load to Eagle Lake is 560 tons per year.  The estimated, non-inventoried, legacy sediment is 2,240 total tons.

Drainage - Our Source of Water

Eagle Lake receives rainfall runoff from two major drainage areas:  a tributary drainage area, and a direct drainage area.  The tributary drainage area is located in the eastern part of the watershed area and includes a network of man-made channels and ditches traversing the watershed, collecting and transporting surface water runoff from the land to the lake.  The tributary channels also serve to collect and transport water for crop production.  The tributary channels and ditches maintain a continuous flow of water throughout the year during periods of normal rainfall.  Surface water runoff from the direct drainage basin to Eagle Lake flows overland and enters the lake directly or is detained or stored in wetlands located directly adjacent to the lake.  A minor tributary drainage area, Oakcrest Creek, in located near Michael’s Restaurant.  The direct drainage basin includes the lakeshore areas.  Surface water leaves Eagle Lake over a dam on the western border of the lake and flows through a constructed channel, named Eagle Creek, and eventually flows into the Fox River, just south of the Village of Rochester.  Groundwater discharge to the surface was observed in several locations throughout the watershed.  This observation would suggest that Eagle Lake receives groundwater discharges or discharges from perched water tables throughout the year (Eagle Lake is not spring fed).
 
Drainage Commission
The modern system of drainage districts and county drainage boards was formalized in 1963 with the creation of Chapter 88 of the Wisconsin Statutes, which became effective on January 1, 1965.  This legislation combined all formal drainage organizations under the same regulatory review.  Further legislation in 1991 required all drainage to come under the jurisdiction of the county drainage board and mandated that the Department of Agriculture, Trade and Consumer Protection (DATCP) establish rules for the operation of drainage districts.
 
Nonpoint Pollution
Nonpoint source water pollution (NPS) is runoff pollution that occurs when rain washes pollutants off the land, out of the air, and runoff carries these pollutants into a water body.  The most common runoff pollutants entering Eagle Lake are sediment, nutrients, bacteria, toxic chemicals, and chlorides.  Although we are largely surrounded by agriculture, runoff from lakeshore properties can also impact lake health.

Wetlands and the Dam

In the past, wetlands in the Eagle Lake Watershed were not recognized for their important values and functions and therefore many have been drained and converted to agricultural use or filled for construction of houses, commercial sites, and highways.  Wetlands can intercept runoff from surfaces prior to reaching open water and remove pollutants through physical, chemical, and biological processes.  Riparian wetlands and marshes located at the margin of lakes protect shorelines and streambanks from erosion. The roots of wetland plants hold soil in place and can reduce velocity of stream or river currents.
 
Approximately 515 acres of impaired wetlands remain viable in the watershed and perform valuable functions for Eagle Lake.  Evaluation of the current health of these wetland areas is among the objectives of the Eagle Lake Protection Program.
 
The Eagle Lake Dam
The Eagle Lake dam is owned by Racine County and is considered a low hazard non-adjustable dam by the Wisconsin DNR.  The dam receives an in-depth inspection once every ten years, with the next inspection scheduled for 2027.  The most recent construction of the Eagle Lake dam was in 1986.  (Source. Gemini AI)
 
The question of raising the height of the dam often surfaces during seasons with lower-than-normal water levels.  We could, in theory, raise the dam's level, but this would require consent from every lakeshore property owner.  However, there are properties along Lakeshore Drive near Peninsula Drive in the Manor that were built in low-lying areas prone to occasional flooding.  Increasing the dam's height would likely worsen flooding for these properties, making it unlikely that their owners would agree to the change.  With this in mind, any discussion of altering the dam is outside of the scope of the Eagle Lake Protection Program.

Historical Water Quality Assessments

The Eagle Lake Management District (ELMD) plays a vital role in maintaining the lake’s health through activities such as weed harvesting, chemical spraying, shoreline cleanup, and managing the Clean Boats Clean Waters program.  Their ongoing collaboration with the Wisconsin DNR and the Racine County Land Conservation Division has made ELMD an indispensable part of lake management efforts, and the community is fortunate to benefit from their dedication.
 
 
From 1993 to 2012, the USGS and Eagle Lake Management District monitored Eagle Lake's water quality, measuring factors like dissolved oxygen, temperature, pH, specific conductance, water clarity, total phosphorus, and chlorophyll-a concentrations.  Key findings during this period include:
 
  • Moderate to poor water quality, with the lake classified as eutrophic.
  • Elevated phosphorus and chlorophyll levels, indicating a high risk of algae blooms.
  • An average Secchi disk reading of 4 feet, reflecting limited water clarity.
  • Invasive species, such as Eurasian Watermilfoil and Curly-leaf Pondweed, were predominant.
In 2016, Eagle Lake was added to the Impaired Waters list for the State of Wisconsin due to excessive nutrients and poor quality of runoff from agricultural areas.  Water quality monitoring resumed in 2018 through DNR grants and the Citizens Lake Monitoring Network (CLMN), focusing on water clarity, phosphorus, and chlorophyll sampling.
 
Water quality in Eagle Lake varies yearly due to a combination of in-lake and external environmental factors.  Long-term monitoring is essential to average out fluctuations and identify trends.  A new water testing program, initiated in spring 2023 and continuing through 2025, has revealed a consistent increase in nutrient levels in the lake since monitoring began.
 

Trophic State of Eagle Lake

Secchi depth, total phosphorus (TP), and chlorophyll-α (chl-a) are key indicators of a lake's trophic state, which reflects its nutrient levels and biological productivity. These metrics can be used to calculate a Trophic State Index (TSI), measuring the total biomass in a water body at the time of sampling.
 
The TSI scale ranges from 0 to 100, with higher values indicating greater biological productivity:
 
  • Oligotrophic (TSI 0-40): Low productivity, clear water, good quality.
  • Mesotrophic (TSI 40-50): Moderate productivity, fair quality.
  • Eutrophic (TSI 50-70): High productivity, poor quality.
  • Hypereutrophic (TSI 70-100+): Extremely high productivity, very poor quality.

The TSI offers insights into a lake's condition, including:
 
  • Water Quality Assessment: Evaluates the lake's overall health.
  • Ecosystem Management: Guides lake management and restoration strategies.
  • Algal Bloom Prediction: Higher TSI values signal a greater risk of algal blooms.
  • Fisheries Management: Supports decisions on fish stocking and habitat management.
 
Looking At Trends for TP and TSI
Decades of data reveal concerning trends in Eagle Lake's water quality.  Both total phosphorus (TP) levels and Trophic State Index (TSI) values show significant, negative trajectories, as illustrated in the accompanying graphs.  Without fundamental changes to the lake and its watershed, the lake's health will continue to deteriorate, jeopardizing its ecological balance and diminishing enjoyment for future generations.
 
 
 
 
 
From the WDNR - Eagle Lake TSI
 
Year 1990 - TSI 60-70
Eutrophic
Blue-green algae become dominant and algal blooms are
possible, extensive plant overgrowth problems possible
 
Year 2024 - TSI 70-80
Becoming hypereutrophic
Heavy algal blooms possible throughout summer, low oxygen levels,
dense plant beds and low visibility (blue-green algae block sunlight).
 
 
 
 
You did it!   That was a lot of material, but you've reached the bottom of this webpage!  Having delved into these topics and gained a deeper understanding of our environmental history, it’s clear why the community's concern has driven the creation of the multi-year Eagle Lake Protection Program.  While the challenges are complex, increased awareness, engagement, and advocacy from the community can pave the way for meaningful, positive change.
 
 
Thank you for visiting CHAPTER 1 of our educational series,
“Ten Things You Should Know About Eagle Lake’s Environmental Challenges."