SUMMARY
The distribution of the phytoplankton community in different locations of Puah Reservoir, Malaysia was investigated from May to December 2019 to examine the phytoplankton compositions and density. Seven sampling locations were selected namely Terengganu Mati (P1), Limbing Besar (P2), Temba Outlet (P3), Pela-gong (P4), Sireh (P5), Centre Dam (P6) and Power Intake (P7). A total of 543 cell/mL were recorded from 35 genera in the reservoir. These identified species belonged to six major plankton groups: 12 green algae (35.29%), nine blue-green algae (26.47%), nine diatom (23.53%), two golden algae (5.88%), two filamentous (5.88%) and one flagellate (2.94%). During this period, Chlorophyta was the most abundant group (40% of the total phytoplankton), followed by Bacillariophyceae (29%), Pyrrhophyta (19%), Cyanophyta (12%) and Chrysophyceae (1%). The highest composition of phytoplankton was recorded at P7 (32%), followed by P3 (16%), P1 (14%) and P4 and P2 with the lowest (8% and 7%), respectively. The lowest density was observed during dry season (162 cell/mL) and high density during wet season (412 cell/mL). Species richness was discreetly greater in the wet season however, evenness index was =0.8, thereby indicating a similarity in species abundance. The water temperature, pH and dissolved oxygen correlate positively with phytoplankton at P = 0.01. The overall mean values of temperature for wet and dry season were 29.3 ± 1.79 °C and 27.5 ± 1.55 °C while dissolved oxygen (DO), biochemical oxygen demand (BOD), chemical oxygen demand (COD) and total suspended solid (TSS) were 16.2 mg/L and 4.7 mg/L, 3.4 mg/L and 2.9 mg/L, 15.2 mg/L and 12.7 mg/L, and 0.5 mg/L and 2.3 mg/L, respectively. Water transparency, pH and DO were found to be important factors characterising each sampling location.