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In the Nebraska Sandhills, there are an estimated 175 square miles of shallow lakes and ponds, about 100 square miles of marsh, and more than 1,500 square miles of subirrigated meadows. These water-dominated landscape features make the Sandhills the second most productive waterfowl region in the United States. Lakes and wetlands occur where lowlying, flat valley floors between grass-stabilized sand dunes intersect the vast groundwater resource of the High Plains, or Ogallala, Aquifer. There is little or no surface water runoff into these lakes. Sandhills lakes range in size from less than 10 acres to more than 800 acres. Lake areas fluctuate seasonally, depending on the dynamic interaction of climatic and hydrologic processes. The deepest Sandhills lake is Blue Lake in Garden County, which is about fifteen feet deep. More characteristic depths are between two and four feet.
Chemical data indicate that the lakes are compositionally diverse, ranging from fresh to brine (total dissolved solids vary from less than 200 milligrams per liter to more than 100,000 milligrams per liter). Alkalinity, as calcium carbonate, ranges from less than 200 to greater than 100,000 milligrams per liter; pH is usually greater than 8.0. Groundwater, primarily derived from local precipitation, is the principal source of water and dissolved solids for the lakes. Differences in the chemistry between lakes are a function of local hydrologic variability, related to the magnitude of inflow and outflow of water from a lake and the age of the lake.
See also PHYSICAL ENVIROMENT: Sandhills.