Water Sources
Surface Sources
Rivers
Bisecting the central part of the state flows the Missouri River, the largest River in North America. It flows southeasterly from North Dakota following the western and southern edges of terminal moraines deposited during the Wisconsin glaciation period. There are numerous rivers which drain the landscapes in eastern South Dakota the largest of which are the Big Sioux and James River which flow south eventually draining into the Missouri River. In western South Dakota, the largest rivers are the Grand, Moreau, Cheyenne, Bad, and the White Rivers which drain older landscapes dissected and carved by erosion. They usually flow east draining into the Missouri River.
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Glacier Lakes
The landscapes of eastern South Dakota were formed by multiple advances of glaciers in the recent past. As the ice melted, lakes were formed on the lower part of the landscape in which drainage was restricted. Their depth depends upon climatic factors, so they are not a reliable long-term source of water for population centers. However in wetter times they can resupply ground water sources, provide water for livestock, and support recreational sports activities.
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Subsurface Sources
Eastern South Dakota has an extensive aquifer system that can be as shallow as 2' or as deep as a few hundred feet. Most cities in eastern South Dakota and many private homes and ranches derive their water supply from one of these aquifers.
In western South Dakota, the accessibility of the ground water is not as good. Some wells are 100's -1000's of feet in depth. The temperature of these water sources can be as high as 125oF. Often, the water quality is marginal since the well may draw water from older marine deposits that contain a high salt content