During a period of nine years, from 2000 to 2008, two consecutive studies—one focusing on observations of adult Odonata, the other on collection of larvae—were carried out in the basin of the Guadiamar River in the southwestern Iberian Peninsula. In addition to monitoring Odonata, several environmental variables were assessed, including an index based on macroinvertebrate communities (IBMWP). In April 1998, this river system suffered from an accidental release of a large mass of toxic mining waste, which exterminated macroinvertebrates in the middle and lower parts and floodplain. Several years later, dragonfly communities in these areas were similar to those of unaffected upper reaches. Communities of sites less affected by general human impact were dominated by semivoltine anisopterans. In contrast, headwaters and river reaches where riparian forest had been destroyed many years ago and seasonality of river discharge was boosted by landscape management harboured chiefly uni- or bivoltine species, regardless whether a site had been affected by mining waste or not. Species assemblage was especially poor in lower river reaches that experienced permanent, diffuse urban and agricultural pollution. A few partivoltine species were recorded, but only in habitats with a high IBMWP index. It seems that over the long term, Odonata respond more to land use and catchment management than other groups included in the IBMWP index.