Aim and Background: It is essential to pay attention to the quality of water for the continuation of human life. Water resources are one of the basic foundations for sustainable development, and in recent years, extensive research has been carried out on water quality assessment. One of the key issues in exploiting water resources is the quality that otherwise would have unexpected consequences in the agriculture, drinking and industry sectors. Mahabad River, located in Mahabad plain, is one of the most important rivers in the West Azerbaijan province. The average annual catchment area of the Mahabad River catchment area is 806 square kilometers and 295 million cubic meters respectively. In this research, the water quality of Mahabad River has been studied from the point of view of some microbiological parameters and the rate of self-pollination of the river. To achieve this goal, international standards for drinking water and irrigation were used.

Materials and Methods: In the present study, which is descriptive-cross sectional, sampling during 6 months from 4 stations consisted of the station 1 km 20 of the Mahabad dam (upstream of Kowsar village), the station number two km 15 of Mahabad dam (upstream of the village of Dehbakr), respectively. Station No.3 km 10 of Mahabad Dam and Station No. 4 km5 of Mahabad Dam were used and MPN method was used to measure water pollution index bacteria. 

Results: Seven biological parameters including diatomaceous earth, chlorophyce, cyanofisce, pertussu, rotifer, chrestas, nematode, residual chlorine, probable value, confirmation and heparin were measured. The results of the data analysis indicated that the river's microbial load was high. As the number of coliform bacteria in stations 1 and 4 was higher than the standard in most of the sampling.

Conclusion: The results of the MPN calculations showed during the research, The microbial load of the river from station 1 to 4 is decreasing due to the flow of movement and its self-propagation.