Palas Basin is a semi-arid closed basin located in the Central Anatolia region of Turkey. The major economic activity in the basin is agriculture; therefore, both surface water and groundwater are used for irrigation. However, intensive use of water resources threatens the hydrologic sustainability of an ecologically important lake ecosystem (Tuzla Lake) located in the basin, as it is hydrologically dependent on surface and groundwater flows from the basin. In this study, we analyze the relationships between agricultural water uses in the Palas Basin and water flows in to the Tuzla Lake using groundwater flow model developed with the FREEWAT platform. The model grid with 250 m x 250 m resolution was created based on the entire watershed, where two hydrostratigraphic units were identified. The source terms defined to the model were rainfall recharge and the sink terms were evapotranspiration and groundwater abstraction from wells. The model was run for one year at steady-state conditions. The model successfully simulated the direction of groundwater flow and groundwater levels in the basin. Annual groundwater recharge was simulated as 5.27 million m(3). Groundwater losses were due to pumping (1.49 million m(3)/yr), leakance to Degirmen River (2.25 million m(3)/yr) and seepage to Tuzla Lake (1.53 million m(3)/yr). Three scenarios were simulated to understand the effect of groundwater use on the lake hydrology. The first scenario assumed that there was no groundwater abstraction. As the second and third water management scenarios, the model was run with 50% less and 50% more groundwater abstraction than that of the current conditions. Water flows to Tuzla Lake were significantly related to groundwater abstraction rates. Increasing groundwater pumping rates reduces groundwater flows to Tuzla Lake and lowers lake water level. No groundwater abstraction and reduction in groundwater pumping rates increase water flows to Tuzla Lake and allow higher lake water levels. This analysis showed that protection of hydrologic characteristics of Tuzla Lake is only possible with more control on groundwater abstraction.