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Mendoza is the province that has the largest irrigated area in Argentina where water resources depend mainly on snowmelt and glacier melting in the closed Andes Mountain. In this region the Blanco River Basin is one of the most important, covering about 300 km2 flowing from the highest peaks to Potrerillos Dam (1300 masl). The objective of this work was to make a preliminary characterization of stable isotopes in surface and groundwater, ice and snowmelt to contribute to a better understanding of the hydrologic cycle in the region, using a Los Gatos DLT-100 analyzer. Hydrochemical analyses were performed on 157 samples. The isotopic composition of rain water is more enriched than streamwater, clearly indicating that the stream recharge sources are at higher altitude. The discharge regime of the streams indicates that snowmelt is the main water origin, and considering the theoretical evolution of isotopes in meltwater, the composition of streams corresponds to the first meltwater, without fractionation. Then, it is more depleted than the original snow. The ice isotopic composition is more enriched than streamwater, indicating that snowmelt is the main recharge source. The hydrochemical results indicate the importance of geology in determining streamwater composition, which is integrated with isotopic data to achieve a better comprehension of the hydrological system. [ABSTRACT FROM AUTHOR]