The current study seeked to monitor five selected stations in the Shatt al-Arab River using the organic pollution index (OPI) and the presence and abundance of two species of snails, Melanoides tuberculata and Neritina violacea. The temperature values ranged from 12.2- 27.5°C, and the salinity ranged from 0.7- 6.79ppt. Whereas, the pH values fluctuated between 6.5 and 8.4. For the biological oxygen demand (BOD5), values were recorded, with the highest values being 6mg.l-1 at the fifth station. Nitrate values ranged from 0.012 to 4.95μg/ l, and phosphate values ranged from 0.11 to 0.589μg/ l.. The average organic pollution index values were registered, with the highest rate at the fourth station (4.19) and the lowest at the first station (1.65). The monthly values of the density of M. tuberculata per square meter ranged between 192 and 16 individuals/ m². The annual average density of M. tuberculata (Individual/ m2) ranged from 120 for the first station to the lowest density of 36 for the third station. While, for the second species, N. violacea, the highest values at the stations reached 96, 120, 96, 50, 48 individuals/ m2, respectively, during November. In addition, no individuals were recorded during July at all stations; the average annual density of N. violacea was between 47.33 individuals/ m2 at Garmat Ali and 13 individuals/ m2 at Hamadan station. It was found that individuals of the M. tuberculata species are denser than the N. violacea species for all stations; the former species is also affected by temperatures more than the second species, therefore the highest density was noticed in the autumn and spring seasons. The non-populated stations recorded less organic pollution than the rest, as an inverse relationship was found between the annual rates; for OPI water, the annual average density of M. tuberculata was greater than that of the second species.