Terminal lakes in arid regions are characterized by increasing concentrations of total dissolved solids (TDS) and decreasing lake volume due to evaporation. Addition of dissolved solids (ions) to lakes threatens the survival of fish species, which in turn adversely affects the surrounding habitats and wildlife that are dependent on these lakes. Over the past 90 years, the stage of Walker Lake, a terminal lake in western Nevada, has decreased more than 40 m while TDS concentrations have increased more than fivefold. A major source of dissolved solids to the lake is the Walker River. TDS entering Walker Lake from the river each year depends on annual flows. When annual flows exceed 93 x 10⁶ m³ (75,000 acre-ft/yr), the relationship of TDS to flow is one of hysteresis; TDS concentrations are higher during increasing flow and lower during decreasing flow. A time-series model of TDS as a function of discharge can be used to simulate observed hysteresis patterns. In addition, the model can be used to better understand and predict river quality and TDS loading to Walker Lake. Dilution of the lake water with low concentration discharge from the Walker River is likely the best method for reducing TDS to Walker Lake; therefore determination of salt load is key in maintaining lake water quality.