Fish can harbour and spread pathogenic bacteria that form the natural micro-flora of the environment, but the flora may be altered by man’s activities such as sewage effluent disposal. The aim of this study was to isolate, identify and enumerate bacteria associated with the different organs of Oreochromis niloticus in Lake Chivero, Zimbabwe and compare their diversity and prevalence. Bacteria were isolated, identified and enumerated from the gills, intestine, kidney, liver, muscle and skin of thirty (30) fish using the culture-based technique on selective and non-selective media. A total of twelve (12) bacteria were isolated, namely Acinetobacter spp., Aeromonas spp., Bacillus subtilis, Citrobacter spp., Edwardsiella tarda, Enterobacter spp., Escherichia coli including E. coli O157:H7, Klebsiella spp., Listeria ivanovii, Shigella spp., Staphylococcus spp., and an unidentified isolate. Staphylococcus spp. were most prevalent on primarily all organs with prevalence rates ranging from 53.3% to 100%. Escherichia coli O157:H7 was least prevalent and was not detected on intestine, liver and kidney. Staphylococcus spp. was the most abundant isolate (1.46 x 105 ± 4.014 x 104 cfu/g) on the skin whereas E. coli, L. ivanovii and Shigella spp. were absent on the kidney. Fish pathogenic bacteria (Aeromonas spp. and Edwardsiella tarda) did not vary significantly in their distribution between the organs (p > 0.05), though high counts were recorded on the gills. Opportunistic pathogens of fish and humans, were significantly high on external organs mainly the skin and gills. The high bacterial infection levels indicate that the fish are heavily stressed and this may negatively impact the populations of O. niloticus in Lake Chivero. The several human pathogenic bacteria isolated render O. niloticus unfit for consumption according to the CODEX Alimentarius standards and pose health risks to consumers.