In 1994, Illinois EPA listed 50.75 miles of Silver Creek as impaired by farm pollution. 28 years later, Illinois removed the creek from its impaired list in 2022

For nearly three decades, a 50.75-mile stretch of Silver Creek in southwestern Illinois remained on the state’s list of impaired waters. Agricultural runoff, erosion, sediment and nutrient pollution had contributed to problems with nitrogen, sedimentation and dissolved oxygen. By 2022, however, monitoring showed enough improvement for Illinois to remove Silver Creek from the Clean Water Act Section 303(d) list for those impairments, as per Illinois Environmental Protection Agency.

What was polluting Silver Creek?

Silver Creek runs through the Wendell Branch-Silver Creek watershed, an area where cropland is the dominant land use. Erosion and nutrient loss from agricultural activity, along with hydromodification, were identified as major sources of nonpoint source pollution.


Sediment and nitrogen from agricultural land had contributed to the creek’s impaired status since 1994. Dissolved oxygen was later added to the list of concerns in 2018.

The Illinois EPA Surface Water Section conducted monitoring in 2011 and 2019, while additional information came from a U.S. Geological Survey monitoring station in 2018 and 2019, as per U.S. Environmental Protection Agency, Grants Reporting and Tracking System (GRTS).

For nitrogen, the creek needed to remain below 7.8 milligrams per liter for nitrate and nitrite in the applicable results. Sedimentation would no longer qualify as an impairment if more than half of the stream bottom was not covered by silt, mud or similar fine sediment. Dissolved oxygen also had to remain at or above 5.0 milligrams per liter.

How did the watershed begin to recover?

A major effort took place between 2016 and 2018, when HeartLands Conservancy led a water-quality improvement project in Madison County.

The work followed projects identified in the 2015 Upper Silver Creek Watershed-Based Plan. Funding for that plan came through a Clean Water Act Section 604(b) grant, while the 2016 Upper Silver Creek BMP implementation project received funding through a CWA Section 319 grant.

The work focused on best management practices designed to tackle erosion, sediment and nutrient pollution before those pollutants could reach Silver Creek.

The projects included an agricultural livestock waste management system, grassed waterways and ponds, streambank and stream channel stabilization, water and sediment control basins, and grade control structures.

The scale of the work was substantial. Four grade stabilization structures were installed, along with 7.9 acres of grassed waterways and two ponds. The project also included 8,140 feet of stream channel stabilization, 505 feet of streambank and shoreline protection, one waste management system and 11,180 feet of water and sediment control basins.

Local landowners also played an important role by helping fund construction on their properties and agreeing to maintain the improvements.

What changed by 2022?

The results were clear enough for the Illinois EPA to reassess Silver Creek in 2022.

Data from the USGS monitoring station showed dissolved oxygen concentrations staying above the required 5.0 mg/L minimum. Illinois EPA monitoring also found nitrate and nitrite concentrations low enough to support removal of the nitrogen impairment, with levels below 7.8 mg/L in all but one sample.

Sedimentation and siltation were also removed as an impairment after observations showed that the stream bottom had sufficient clearance from silt, mud and other fine sediment.

The improvements were attributed in part to the BMPs installed throughout the watershed, which targeted the main sources of pollution.

According to the supplied project results, the work led to estimated annual reductions of 2,678 pounds of phosphorus, 7,054 pounds of nitrogen and 2,699 tons of sediment entering the watershed.

The Silver Creek watershed plan continues to address other water-quality concerns, while the Illinois EPA and local watershed partners continue monitoring the area.

For Silver Creek, the change from an impaired waterway in 1994 to removal from the state’s impaired list in 2022 marked the result of years of monitoring, watershed planning and pollution-control work.

FAQs

Why was Silver Creek listed as impaired?
Farm runoff, erosion, sediment and nitrogen pollution affected the creek, along with low dissolved oxygen.

When was Silver Creek removed from the impaired list?
Illinois removed Silver Creek from the CWA Section 303(d) list in 2022, 28 years after it was first listed.