The benthic fauna of the river Euphrates upstream and downstream sectors of Al-Qadisia dam, mid Iraq, was studied for a period of two years (1993 and 1994). Five sampling stations were selected. One station was located upstream the dam, while the other four stations were downstream. A total of 65 taxa were identified. It was clear that the station located immediately downstream (station 2) showed the highest total mean annual density (individuals/m 2 ) represented by higher number of taxa. The benthic community was dominated by oligochaetes especially of families Naididae and Tubificidae as well as chironomid larvae of which the genus Polypedilum was the most dominant one. Seasonal fluctuation of the community showed that the peak of the total number of individuals had appeared during autumn and winter months. Community index of similarity (ISE) was computed for faunal comparison between station 1 and the other stations.

The benthic fauna of the river Euphrates upstream and downstream sectors of Al‐Qadisia dam, mid Iraq, was studied for a period of two years (1993 and 1994). Five sampling stations were selected. One station was located upstream the dam, while the other four stations were downstream. A total of 65 taxa were identified. It was clear that the station located immediately downstream (station 2) showed the highest total mean annual density (individuals/m2) represented by higher number of taxa. The benthic community was dominated by oligochaetes especially of families Naididae and Tubificidae as well as chironomid larvae of which the genus Polypedilum was the most dominant one. Seasonal fluctuation of the community showed that the peak of the total number of individuals had appeared during autumn and winter months. Community index of similarity (ISE) was computed for faunal comparison between station 1 and the other stations. © 1998 John Wiley & Sons, Ltd.