The current study included the use of phytoplankton as an indicator to assess the water quality of the Tigris River in the Wana district of Nineveh Governorate/ Iraq, Five sites were selected along the Tigris River, and samples were collected monthly from November 2021 to April 2022. Some environmental factors of water affecting water quality and its characteristics were studied including water temperature, which was suitable for drinking purposes throughout the study period. Its highest value did not exceed 23.8°C; while, the pH was within the permissible limits for drinking water, with values ranging between 7.0 & 8.1. The electrical conductivity recorded values ​​within the normal range; its lowest value was 191 µS/cm, and the highest was 423 µS/cm. The dissolved oxygen results showed that the river water at all the sites under study was well aerated, The concentrations of nitrates and sulfates didn't exceed the limits allowed by the World Health Organization during the study period, as it recorded concentrations that ranged between 0.01-0.52 and 25-114mg/ L, respectively. For the phosphate concentrations in the river water, they had a medium to high effect with ranges between 0.08 & 1.6mg/ liter, and depending on the concentrations of total dissolved solids, the river water was somewhat fresh, The alkaline concentrations in the river water during the study period ranged between 74 &170mg/ l. The chloride ion concentration was wobbling, and the river water was classified as relatively hard to hard water. The total density of phytoplankton exceeded the threshold of half a million cell/ liter.  Applied to a kind of biological indicator of pollution, Palmer's Poitution index (the index of species tolerant to pollution),  showed that the water was possibly moderately polluted during the study period. At all sites under study, the value of the index in the first and fourth sites was (14), while the second site recorded the lowest value of the index, amounting to (13), while the value of the index was (15) in the third and fifth sites, during the study (43) species of algae were detected, in which Bacillus algae dominated.