[en] Approximately 600 000 t of industrial wastes were released into the Flix reservoir (Ebro River, Spain) for several decades containing elevated quantities of organic contaminants, heavy metals and radioisotopes. In particular, production of dicalcium phosphate (DCP) from Morocco's phosphate rock and further processed at the chemical industry located in Flix, ended up with the accumulation of wastes with high concentrations of ²³⁸U and its daughter products (i.e. ²²⁶Ra, ²¹⁰Po, ²¹⁰Pb, etc.) in the reservoir. Maximum specific activities of ²³⁸U and its descendants were found to be in the order of 10³ to 10⁴ Bq/kg, and estimated inventories in the reservoir range from 102 to 103 GBq for each radionuclide. The radiological quantification of these muds led to the initiation of an exhaustive study of its potential mobility and, therefore, the effects through the entire ecosystem in the lower course of the Ebro River (along 98 km). Main efforts focus on the transport of the suite of radionuclides by water under different hydrodynamic conditions and their distribution in the Flix reservoir and the estuarine area. Agricultural soils and fruit and vegetable production are also being analysed, especially at paddy fields and rice seeds located down the river and spread out over the Ebro delta. In an ongoing research ecosystem organisms will be analysed. Macrophytes, phytoplankton, fishes (Cyprinus carpio, Silurus glanis), and others such as river bivalves (Dreissena polymorpha) and birds, shall let us gauge radionuclide dispersion through the trophic chain, aiming to estimate population exposure in further studies