Water depth in the channel is maintained by three dams in the basin and four dams upstream from the basin. Land use in the study area is primarily agricultural. Corn and soybeans are the major crops in the basin. The 1990 population in the basin was 1.33 million. The climate of the lower Illinois River Basin is continental.
Summers generally are hot and humid, and winters are cold.
Mean annual precipitation in the basin is 36 inches. The major aquifers in the basin are composed of glacial deposits of Quaternary age and bedrock of Pennsylvanian to Mississippian age. Many of the major Quaternary aquifers are in buried bedrock valleys. Major Water Quality Issues Major water quality issues in the basin include sedimentation, toxic chemicals in sediment, high concentrations of nutrients and agricultural chemicals, and low dissolved oxygen. Sedimentation has resulted in the partial or complete filling of many lakes in the study area.