The hydrographic network in the Iberian Pyrite Belt (IPB) (south-west Europe) is intensively affected by acid mine drainage (AMD) processes. This represents a unique worldwide scenario of extractive mining activity for more than 4,000 years. In order to be able to achieve possible restorations, it is necessary to reduce the scale of possible actions for future environmental improvements, at the river basin level. Therefore, the delineation of watersheds and subwatersheds in the IPB has been carried out, as well as the definition of the degree of impact by AMD processes in these basins in the dry season and in the rainy season. The results show that all basins are affected by AMD processes during the entire hydrological year, with pH values between 2 and 3, for most cases, and high concentrations of sulfates, metals and arsenic.