Chemometric methods are applied in the analysis and interpretation of large multivariate data sets obtained in environmental monitoring studies. Multiple fish and sediment river samples from different sampling sites at different geographical locations and during different campaigns and/or sampling time periods were collected and analyzed as a part of an extensive multi annual monitoring program. Concentrations of organic microcontaminants (like hexachlorobenzene, hexachloro-butadiene, hexachlorocyclohexane, dichloro-diphenyldichloroethane and metabolites, and polychlorinated biphenyls PCBs, among others) were determined in fish and sediment river samples from Catalonia (northeast Spain). Chemometrics modeling and interpretation of these data sets allowed the investigation of the main contamination patterns in the rivers under study and the investigation of their distribution. The results achieved in this study are intended to be a contribution to quality assessment and evaluation of the global situation of the contamination of surface waters in Catalonia, and to support public policies of environmental control and protection in the region under study.