The Tigris River is the second longest river in West Asia. It passes through densely populated areas, especially in the city of Baghdad. As a result of the demand for water that become at its highest levels. In contrast, the discharge of the Tigris River has decreased, in addition to the poor quality of the water of the Diyala River, which is one of the tributaries of the Tigris River on the Baghdad side, due to the increasing amounts of wastewater in it. And the deficiency and poor quality of wastewater treatment plants, which in turn affects the life balance of living organisms, including phytoplankton, which is considered one of the components of the food chain for living organisms in the ecosystem. Wide differences exist among algal species in their requirements for nutrient metals or in their sensitivity to pollutants and thus the predominant effect of pollutants may well be on species composition of phytoplankton communities. Five sites were chosen (Saeda on the Tigris , Al-Multaqa on Diyala , Al-Tuwaitha on Tigris , Al-Jaara on the Tigris , Jesr Enbopy on Diyala) from which samples were taken to measure heavy metals (Zn,Cu, Fe),Chemical Oxygen Demand COD, PH , and phytoplankton were diagnosed in quantity and quality for three season (October , January , March ) Statistical techniques were applied and Shanon-Weiner diversity index(H) to evaluate the changes during the three seasons, and the results that the phytoplankton species showed a dominance of Cyanophyceae in quantity and quality in the study seasons is followed by Chlorophyceae and then Baciliariophyceae in quantity. As for quality, Cyanophyceae is followed by Baciliariophyceae and then Chlorophyceae with low specific density and high diversity according to the Shanon-Wiener index only in Autumn with a high diversity of 3.39 at site 2 of the Diyala River, followed by Spring with a diversity of 3.115 at site 1 of the Tigris River, And the highest biomass of phytoplankton was in the Autumn and the lowest biomass was in the Spring.