Water Quality Testing History
 
The Eagle Lake Management District (ELMD) plays a vital role in maintaining the lake’s health through weed harvesting, chemical treatments, shoreline cleanup, fish stocking, the Clean Boats Clean Waters program, and other initiatives. We thank our volunteer ELMD Commissioners for their dedication to Eagle Lake!
  
From 1993 to 2012, the USGS and ELMD 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.
 
In 2023, ELIA raised money from the community to initiate the Eagle Lake Protection Program (ELPP), a three-year water and sediment testing program, in collaboration with Dr. Marcel Dijkstra of UW Oshkosh. Dr. Dijkstra's final report issued in June 2026 confirms the continued increase in nutrient levels Eagle Lake.
 
Eagle Lake is Hypereutrophic
 
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 and a greater risk of harmful algal blooms:

 

• 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.  

 
Eagle Lake TSI is Getting Worse

 

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 graphs below. 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.

 
 
 
 
 
1990s TSI 60-70: Eutrophic
Blue-green algae become dominant and algal blooms are possible, extensive plant overgrowth problems possible
 
2020s TSI 70-80: Hypereutrophic
Heavy algal blooms possible throughout summer, low oxygen levels, dense plant beds and low visibility