The effect of human activities and oil pollution on the microbiological quality of Udu River was investigated from September 2002 to January 2003. The microbiological parameters were carried out using the standard microbiological techniques. The bacterial and fungal loads were shown to be highest in the inhabited stations (2 and 3) with downstream (station 4) suffering from dilution effects of human activities and upstream (station 1) showing lower counts. Stations 2 and 3 were shown to record the highest heterotrophic microbial load 10.7 x 108 cfuml-1 and 10.4 x 108 cfuml-1 and 8.0 x 108 cfuml-1 and 9.0 x 108 cfuml-1 for bacterial and fungal isolates respectively. Total coliform counts ranges from 1.5 – 4.3 x 106 and 1.4 – 2.8 x 106 MPN100ml-1 for stations 2 and 3. Microorganism isolated and characterized includes nine bacterial and four fungal genera. The bacterial isolates were Staphylococcus, Streptococcus, Proteus, Escherichia, Clostridium, Acetobacter, Salmonella, Pseudomonas, Micrococcus, and the predominant fungal isolates includes, Aspergillus, Penicillium, Geotrichum and Helminthosporium. The concentrations of total suspended solids, biochemical oxygen demand (BOD5), conductivity, total iron, total solids, total copper and total dissolved solids were shown to be higher in stations 2 and 3 than station 1 which have no direct human activities. Similarly, the values obtained for salinity, total hardness and dissolved oxygen (DO) of the inhabited stations were shown to be lower than station 1. Correlation coefficient shows positive relationship between the different microbial populations and some physiochemical parameters studied.

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