[EN] The purpose of this study was to examine the nature and magnitude of the thermal inconsistencies ocurring in the surface waters of the River Ebro Basin (NE Spain). The relationship between air and water temperatures, established using data of 60 monitoring stations, the variation of water temperature with altitude, the quantity of heat annually transported by water at the sampling points, and a heat balance for the River Ebro from source to mouth were used as the mean criteria to identify sites having and irregular thermal behaviour.