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The water quality of the rivers is a general concern. In 2008, water samples were taken from the Santa María River near Ingenio La Victoria in 10 different sites. The objective of this study is to establish the quality of the waters in the lower middle basin of the river. Physicochemical and microbiological analyses were run to the samples. Physicochemical analysis included pH, conductivity, STD, water temperature, dissolved oxygen and turbidity. Microbiological testing included detection of total and fecal coliforms and aerobic counts. To detect and quantify total coliforms and Escherichia coli Petrifilm plates were used 3MEC while Petrifilm plates for aerobic bacteria were used 3MAC. Separating the data by time of year, the sampling sites were compared and it was found that during the rainy season significant differences (P < 0.05) between sampling sites were observed in the variables conductivity, turbidity and STD; and in the dry season differences in STD was observed. Some results presented concern dissolved oxygen minimum values. When comparing all data by time of year it was determined that the physicochemical variables pH, conductivity, STD and showed higher values ??during dry season; and turbidity was higher in the rainy season. In bacteriological counts, aerobic counts and total coliforms did not differ; while fecal coliforms were higher in the rainy season.The section of the river maintains acceptable levels in the parameters studied.The results indicate that microbiological and physical - chemical contamination is occurring and their levels, although acceptable, are increasingly detectable; which reflects the affectation by human activity.