Irrigated agriculture notably increases crop productivity but may negatively impact river water quality because of the salt and agrochemical loadings in irrigation return flows. We evaluated the salinity and ion concentrations in 31 river stations of the Ebro basin, characterized the quality of waters for irrigation, and analysed the influence of irrigation on river water quality. River water quality is generally good in regard to salinity (EC), NO₃ and PO₄ concentrations, and water quality for irrigation of the most important schemes within the Ebro basin is excellent for crops although it may promote the degradation of sensitive soils. A preliminary analysis of the impact of irrigated agriculture on river water quantity and quality indicates that it is significant in rivers collecting high salt and NO₃ irrigation return flows. Nevertheless, due to the low salinity of most irrigation waters, maximum irrigation efficiencies are attainable in the Ebro basin without compromising crop yields due to root zone soil salinization.