Rivers and streams are created from runoff and water that seeps into and is now coming up out of the ground. The fast-moving action of rivers and streams causes the mixing of water and air, which allows oxygen to be dissolved into the water. This process, aeration, gives rivers and streams the oxygen levels they need to support wide varieties of life. Life forms found in healthy rivers and streams include plants, algae, fish, insects, amphibians and reptiles. The health of a river or stream can be determined by the diversity and types of species found in the water.

Wetlands are lowlands that are periodically covered with water. They keep surface waters clean by filtering out sediment and trapping pollutants. Wetlands have traditionally been regarded as wastelands; since colonial times, over half the wetlands in the United States have been destroyed. But new federal and state regulations are protecting wetlands.

People also realize the importance of wetlands, and are voluntarily protecting these valuable areas on their own property. Portions of Montana, North Dakota, South Dakota, Minnesota and Iowa lie within the prairie pothole region. Prairie potholes provide the second largest source of fresh water behind only the Great Lakes. South Dakota's conservation districts are partnering with the US Fish & Wildlife Service to create and protect wetlands.

Groundwater is the water that seeps into the ground after rain or snow melt. The amount of water that seeps into the ground varies from place to place depending on the slope of the land, amount of rainfall, soil type and land surface. Over half of the fresh water on earth is stored as groundwater.

Aquifers are underground rock zones or soil layer that contains usable amounts of groundwater. The amount of water stored in an aquifer depends on the type of soil. Mixtures of sand, clay and fine particles yield small amounts because these materials don't allow water to absorb and flow. Learn more about groundwater aquifers and South Dakota's aquifers.