Illinois River

According to the USGS’s Lower Illinois River Basin National Water Quality Assessment program, there are problems with water quality. Concentrations of nitrate and agricultural chemicals exceed maximum contaminant levels established by the USEPA. In 1990, approximately 9 million pounds of atrazine are applied in Illinois; this is one-sixth of the national total and more than any other state. Dissolved oxygen levels also drop below the minimum of 5 parts per million (ppm) aquatic life criteria set by the USEPA. In 1988, dissolved oxygen levels are recorded at 2 ppm.

The USGS’s circular 1209 (2000) reports the status of water quality in the Lower Illinois River Basin from 1995-1998. During this period, the water quality of the larger rivers such as the Illinois and Sangamon are more likely to meet drinking water standards than the smaller streams. In the spring, concentrations of nitrates in the smaller streams exceed the Maximum Contaminant Level (MCL) of 10 milligrams per liter (mg/L).

Nitrogen and phosphorus concentrations here are among the highest in the nation. The MCL for nitrate is exceeded in 15% of all samples taken. The concentration of total phosphorus in 79% of the samples exceeds the 0.1 mg/L guideline recommended by USEPA. The Illinois State Water Survey (ISWS) documents these concentrations and portrays them by county in maps (Figures 42 and 43).

The 2000 USGS report also finds that three herbicides commonly used by farmers, atrazine, metolachlor, and cyanazine, are detected in every sample collected during the reporting period. In the spring, these chemicals run off into water bodies, resulting in levels that exceed drinking water standards. The chemical acetochlor is detected in most samples, 81%. Organochlorine compounds (including insecticides no longer used) are detected in fish and tissue and sediment.