Abstract

This study presents a compilation of phytoplankton species composition of Esa-Odo reservoir, Osun state, Southern Nigeria. Three sampling stations (Stations 1, 2 and 3) were established at the inflow of the reservoir, the mid basin portion, and the outflow very close to the dam site along the horizontal axis of the reservoir. Samples collection spanned a period of nine (9) months (February to October, 2017), covering both dry and rainy seasons. The phytoplankton samples collected were examined, recorded, measured, photographed and enumerated with a light compound microscope (Olympus599807) at the Institute of Ecology and Environmental Studies, Obafemi Awolowo University, Ile-Ife, Osun State.  The results showed that a total of one hundred and forty three (143) species of phytoplankton recorded belonged to sixty four (64) genera, forty (40) families, twenty-eight (28) Orders, ten (10) classes and seven (7) Divisions of Algae as summarized in (Table 1). Cyanobacteria were the phytoplankton group found in the highest percentage (48%) of occurrence in total phytoplankton population, while Ochrophyta had the lowest percentage (1%) occurrence. Bacillariophyta had the highest abundance of species and were the dominant genera across the upper, middle and lower basins of the reservoir.