The Illinois Watershed (HUC 11110103) covers approximately 6,897 square miles in northern Illinois and parts of Wisconsin and Indiana. The hydrology of the area is primarily influenced by the Fox River, Des Plaines River, and Kankakee River. Snowpack in the region varies from year to year, but the area experiences an average of 30 inches of snowfall annually. Surface water in the watershed includes numerous streams, lakes, and wetlands. The region also contains several reservoirs, including Lake Geneva and the Chain O'Lakes. Reservoir constituents include a variety of fish species, such as largemouth bass, bluegill, and walleye. Interesting climatic facts include the area's susceptibility to severe thunderstorms, tornadoes, and flooding. In recent years, the region has experienced increased precipitation, which has led to higher water levels in many of the lakes and rivers.