The study was conducted to measure diatom species diversity in the lotic ecosystem across the Wasit Province for 12 months. The quantitative study of diatoms (phytoplankton) was investigated in the Tigris river. The density of algae was ranged from 60989 cell×103/l to 112780.82 cell×103/l in the five sites. These algae were belonging to 39 genera. The richness index values ranged from 1.53 at site 5 in January 2016 to 6.34 at site 1 and June2015. Shannon-Weiner diversity index (H´) was 2.33 in February 2016 and 3.72 in June 2015 both values at site 3, whereas Evenness index was 0.54 at site 5 in March2016 and 0.98 at site 1 in both August2015 and May2016. The lack of homogeneity of the appearance of species indicates the dominance of a few species with high densities, which is an indicator of the existence of environmental pressure. All studied indices showed that the Tigris River quality is suitable for the living aquatic life or may be slightly affected by the pollutants.

The present study conducted to study epipelic diatoms in the Tigris River within Wasit province for one year from June 2015 to May 2016, five sites have been chosen along the river between Al-Aziziyah and Kut .The aim of the study was to identify and main distributed to them in the Tigris River data were collected by the qualitative and quantitative study of epipelic diatoms. A total number of 161 species of epipelic diatoms was recorded belongs to 36 genera, where the number of central diatoms species recorded were 14 diatoms belonged to 7 genera by (8.69%) and The pinnate diatoms species were 147 species belonging to 27 genera by (91.30%). Seasonal and spatial variations were observed in the total numbers of benthic diatom during the study period, the results recorded the lowest rate of both central and pinnate diatoms were (745.29× 104/cm3) in site1 and the highest rate (1122.92 × 104 /cm3) in site4.Some genera have recorded higher number species during the study period; these genera were Nitzschia, Navicula, Cymbella, Gomphonema, Amphora, Cyclotella, Melosira, Cocconies, Caloneis, Diatoma, Fragiaria, Surirella and Synedra. The study revealed that Bacillariophyceae were abundant, reflecting the quality of water and mud and determine the extent of pollution and polluted type