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ABSTRACT Phytoplankton composition is an important aspect of water quality assessment. According to literature, the presence and abundance of phytoplankton species of certain taxonomic groups in a water body are indicative of its trophic state. This study investigated the phytoplankton community composition and some environmental variables of Okhuiahe River, monthly for a period of six months (November, 2015 - April, 2016). Three stations were chosen along the stretch of the river for surface water collections. Some basic water quality parameters were assessed. Results showed that the parameters did not vary significantly among stations due to the almost constant weather pattern throughout the study period. Findings from the study showed that apart from pH which was fairly acidic, the other parameters (conductivity, total dissolved solids, dissolved oxygen and biochemical oxygen demand) were within the WHO limit for drinking water. The phytoplankton composition of Okhuiahe River during the sampling period was assessed and it comprised 182 species grouped in 5 divisions. The order of dominance in the phytoplankton community composition is Bacillariophyta ˃ Chlorophyta ˃ Cyanophyta ˃ Euglenophyta ˃ Rhodophyta. The abundance of diatoms (Bacillariophyta) and desmids is indicative of low nutrient content and acidic pH as recorded in the study. The occurrence of relatively few cyanobacteria (Cyanophyta) and euglenoids (Euglenophyta) is indicative of low nutrient content as they thrive in eutrophic water bodies rich in organic matter. The presence of only 1 Rhodophyta species, Batrochospermum sp. is not unusual because they are predominantly marine and brackish. Hence, it is indicative of low salinity and this conforms to the fresh water status of the river.
