Illinois has a humid continental climate, with precipitation occurring throughout the year, and an average annual precipitation of 39 inches. There are several major surface flows in Illinois, including the Illinois River, the Mississippi River, and the Wabash River. These rivers are fed by numerous tributaries, including the Kankakee River, the Des Plaines River, and the Rock River. There are also several major reservoirs and dams in Illinois, including the Rend Lake Reservoir, the Carlyle Lake Reservoir, and the Lake Shelbyville Reservoir. The state's hydrology is influenced by snowpack, with heavier snow and ice accumulation in the northern parts of the state. Overall, Illinois' hydrological conditions are heavily influenced by its geography, climate, and precipitation patterns.