<p>Protozoa concentration in the dam water samples.</p>

This study assessed the microbial quality and bacterial diversity in water from Owena multipurpose dam in order to gain a more understanding of the microbial population and potential risks of infection associated with usage of the dam water. Water samples were collected below the surface and near the dam bed biweekly over a six-month period of covering both wet and dry periods. Total viable count, faecal indicator bacteria and protozoa were determined using standard pour plate technique and molecular methods. Risks associated with human consumption of water from the dam were determined using dose-response approach. Results showed that load of E. coli ranged from 3.0 to 4.3 log₁₀ cfu/100 ml, Proteus 3.6 to 4.5 log₁₀ cfu/100 ml and Shigella 3.3 to 4.1 log₁₀ cfu/100 ml. Proteobacteria (57.63%) and Bacteroidota (26.63%) were the most predominant phyla in the water samples. At the order level, Pseudomonadales (40.43%) and Cytophagales (28.29%) were predominant, while Pseudomonadaceae (39.17%) and Spirosomaceae (28.29%) were the dominant family, and Pseudomonas sp003428805 (27.61%) and Arcicella rosea (19.09%) were most prevalent species. Cryptosporidium parvum and Giardia lamblia were detected in 83.33% and 50% of the water samples, respectively. The risks of infection with the pathogens were all greater than 10^-4 and, in this order, Klebsiella < Giardia lamblia < Salmonella < Cryptosporidium parvum < Shigella.. The relatively high load of bacteria and protozoa in the samples suggest continuous contamination. Water from the dam must be adequately treated before consumption in order to protect human health from potential risks of infections.