This study aimed to assess the effect of temperature on the primary productivity of phytoplankton in the waters of Khor Al-Zubair lagoon in Basra City, Iraq, through a seasonal analysis of two stations. Environmental factors such as water temperature, permeability, salinity, pH, nitrates, and phosphates were measured. In addition,  chlorophyll a along with primary productivity were evaluated using light and dark bottles.The results indicated that temperature had a greater impact on primary productivity than other environmental factors, particularly nitrates and phosphates, which were abundantly available in the study area. The highest productivity values were observed during the moderate climate of spring and autumn seasons, with the spring season recording the peak productivity values of 309.37 and 437.5mg C/m³/h for the first and second stations, respectively. The first station was classified as nutrient-rich, while the second station was identified as nutrient-limited during the spring phytoplankton bloom, based on chlorophyll a concentrations.