South Dakota has a humid continental climate with four distinct seasons. The Missouri River, which forms the eastern border of the state, is the largest and most significant surface flow. It is subject to extreme flooding during spring and summer due to snowmelt and heavy rainfall. Other major rivers include the Cheyenne, James, and Big Sioux. The state has several reservoirs and dams, including the Oahe, Fort Randall, and Big Bend dams, which provide flood control, irrigation, and hydroelectric power. South Dakota's hydrology is influenced by its topography, soil type, and vegetation cover, which affect the amount and rate of water infiltration and runoff. The state's snowpack and precipitation patterns are important factors in determining water availability and storage.