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Approximately 2,800 natural lakes smaller than 10 acres in size are found in the northern plains region of Nebraska, South Dakota and North Dakota. Water quality characteristics vary greatly among lakes in close geographical proximity. They range from fresh to highly mineralized bicarbonate-carbonate-hydroxide (alkaline) to chloro-sulfate (saline) types and regionally represent the largest concentration of inland mineral waters in North America. Water quality together with shallow basin morphometry exert major environmental influences on the fisheries in great plains natural lakes.
In the sandhills region of Nebraska (20,000 sq. mi.) only about 45% of the estimated 1,400 natural lakes support fish populations because of the excessive alkalinity content of many lakes. Manageable lakes for sport fishery have a total alkalinity content of < 1,000 mg/1 with a maximum depth > 5.0 ft. Northern pike, Esox lucius, largemouth bass, Micropterus salmoides, bluegill, Lepomis macrochirus, yellow perch, Perca flavescens, black crappie, Pomoxis nigromaculatus, and black bullhead, Ictalurus melas, are the major game fish. "Alkalionic" species, Sacramento perch, Archoplites interruptus, and the fathead minnow, Pimephales promelas, survive in lakes of moderate alkalinities (900-1,800 mg/1). Annual recruitment of above species is normally adequate and hatchery stock is utilized only under renovated and winter-kill conditions.