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The Southern Imera river crosses one of the most arid part of Sicily. The geochemical composition of the river water is due to the solubilization processes of gypsum rocks, which accounts for the particularly low quality of resources in the areas in which the presence of evaporitics deposits is highest. The geochemical composition and hydraulic parameters of river was monitored with the aim of reaching a better understanding of the relationships between litology and water quality. The Imera river is a potential local hydric resource, but seasonal variability of salinity does not allow farmers to use its water. A geochemical monitoring of the Imera river water has been carried out in selected localities integrating a GIS analysis of the river hydrography basin and of the distribution of the evaporitic formation. During 2003 and 2005 we performed four monitoring surveys of water chemicophysical parameters (temperature, pH and electrical conductivity) and of the main ionic concentrations (Ca2+, Mg2+, K+, Na+, Cl-, SO4 2- ). We also installed a multiparameter probe next to the hydrometrical station of Drasi, about 15 km from the river mouth. Such multiparameter probe was used to determine, continuously and simultaneously, temperature, electrical conductivity, pH, dissolved oxygen, redox potenzial, water level. The geochemical composition of the water allowed to confirm the results of Roda (1971) and Favara (2000), who pointed out that the main cause of degrade of the Southern Imera river are the salt-rich waters of some tributaries flowing over gypsum rocks and halite deposits. We have been able to identify which specific areas are the main contributors to the degradation of the Imera river.