Priority Watersheds

What is a watershed?

A watershed is the land where all water drains across the surface or underground toward the nearest water body. In any region, all the water eventually drains to ponds, rivers, lakes, or oceans. Even though watersheds come in different sizes, what happens in one region can impact everything downstream. 

In Illinois, most of the state's land flows into the Mississippi River. This means that our local water quality affects the Mississippi River all the way down to the Gulf of Mexico.  Only a small portion of northeast Illinois drains toward Lake Michigan, so local water quality in the Chicago area can affect Lake Michigan. 

What watersheds does the Illinois NLRS focus on?

Priority watersheds are those expected to have the greatest capacity to reduce high volumes of nutrient losses annually. Illinois prioritized watersheds when developing its Nutrient Loss Reduction Strategy in 2015. The strategy focuses on agricultural watersheds high in total phosphorus loss, agricultural watersheds high in nitrate-nitrogen loss, and point source watersheds high in both total phosphorus and nitrate-nitrogen losses. Watersheds were prioritized based on nutrient loading data, information on local water quality conditions documented in the Illinois Integrated Water Quality Report, and knowledge of watershed-based planning infrastructure.

While all watersheds are important to nutrient reduction goals, the NLRS priority watersheds are targeted for watershed-based planning efforts, funding, outreach, and implementation programs. They are also more closely monitored for nutrient losses. Illinois Extension watershed outreach staff provide focused support for the nitrogen-priority watersheds of Lower Rock River and the Mississippi North Central (Flint-Henderson) and the phosphorus-priority watersheds, Embarras River and the Little Wabash River.

Priority watersheds for agricultural non-point sources

Total Phosphorus 

  • Big Muddy River Watershed
  • Embarras River Watershed
  • Little Wabash River Watershed


  • Lower Illinois-Senachwine Lake Watershed 
  • Lower Rock River Watershed
  • Mississippi North Central Watershed/Flint-Henderson Creek

Explore progress updates for Pine Creek Watershed, Ogle County; Cedar Creek, Warren, Knox, and Henderson counties; Mill Creek Watershed, Rock Island County; and Copperas Creek Watershed, Rock Island County. 

The development of a watershed characterization of the Embarras Watershed, along with plans for two subwatersheds – the Slough Watershed in Lawrence, Richland, and Crawford counties; and Polecat Creek Watershed in Coles and Edgar counties – was completed in 2022. This was an Extension, Illinois Farm Bureau, and Soil & Water Conservation District partnership. The Mississippi North Central Watershed was completed in 2023.


Keep it for the Crop priority watersheds 

In 2011, during development of the Keep it for the Crop program, Illinois EPA and the Illinois Department of Agriculture worked with the Illinois Council on Best Management Practices to identify priority watersheds where implementation and outreach could begin. Two additional watersheds were added to that list in 2013. 

  • Lake Bloomington Watershed 
  • Lake Vermilion Watershed 
  • Salt Fork Vermilion River Watershed 
  • Vermilion River Watershed (Illinois River Basin) 
  • Lake Decatur Watershed 
  • Lake Mauvaise Terre Watershed 
  • Lake Springfield Watershed
  • Evergreen Lake Watershed


Priority watersheds for point sources 

A point source is any site of discharge into a waterway, such as municipal sewage treatment facilities and industrial wastewater treatment facilities. The primary nutrient concern for point source discharge is total phosphorus, and the highest priority watersheds are already the focus of point source reduction efforts for total phosphorus. However, the five priority watersheds for point source contributions are those that rank high in both total phosphorus and nitrate-nitrogen loading:  

  • Upper Fox River Watershed 
  • Des Plaines River/DuPage River Watershed 
  • Upper Sangamon River Watershed 
  • Lower Rock River Watershed 
  • Illinois River-Senachwine Lake Watershed 

Banner image: Prairie Research Institute Illinois State Water Survey,