In order to determine the occurrence of antimicrobial-resistant Enterobacteriaceae, 506 samples of drinking water, surface water, and ground water were studied in the province of Chaco, Argentina. One hundred and ninety one isolates of Enterobacteriaceae Family members were obtained. The most frequent specie was Escherichia coli and it showed the highest rate of acquired resistance, being the ?-lactams the most affected antibiotics. The findings of the present work suggest that the occurrence of antimicrobial-resistant bacteria in aquatic ecosystems of Chaco may contribute to the environmental dissemination of antibiotic resistance.