Illinois possesses one of the most extensive and interconnected river systems in the United States. Major waterways including the Illinois River, Chicago River system, Kaskaskia, Sangamon, and LaMoine flow through densely populated urban areas, intensive agricultural landscapes, and industrial corridors before joining the Mississippi River. This hydrological profile makes Illinois both a significant contributor to, and a downstream recipient of, microplastic pollution.
The state’s combination of major municipal wastewater treatment infrastructure, intensive row-crop agriculture with widespread use of plastic agricultural products, and substantial urban impervious surfaces create micro and nanoplastics (MNP) sources that few other regions match.
The McCormick, et. al (2016) study on nine Illinois rivers established that wastewater treatment plant (WWTP) effluent is a significant point source of microplastic to urban streams, with concentrations consistently elevated downstream of discharge points. This work has informed subsequent research efforts across the state.
Environment Illinois and allied organizations have undertaken expanded statewide sampling projects in 2025 and 2026, surveying microplastic presence across dozens of rivers, lakes, and streams. While comprehensive results are still being compiled, preliminary findings confirm the pervasive presence of MNPs across Illinois water bodies of all sizes and types.
Regional context further reinforces the scale of the problem. A survey by Environment Minnesota found microplastics at every single site studied across the upper Midwest, confirming that contamination is not limited to major urban waterways but extends throughout the region’s freshwater systems. Illinois operates hundreds of municipal wastewater treatment plants. Even high-efficiency plants release significant quantities of MNPs, particularly fibers and fragments. And as a leading agricultural state, Illinois’s extensive use of plastic mulch, silage wrap, irrigation tubing, and polymer-coated fertilizers introduces MNPs directly into farm soils that wash into waterways. In industrial corridors, pre-production plastic pellets, processing residues, and industrial wastewater contribute to MNP loading. Tire wear particles, litter fragmentation, and atmospheric fallout are collected by stormwater systems and discharged, often untreated, into receiving waters.
