Perennial Oued Zegzel and temporary Oued Cherraa are parts of the same watercourse. Coinertia analysis showed the cleardistinction between these two parts and the close relationship of the faunal assemblages with the characteristics of the water. Theheadwater course of the Zegzel is covered with dense terrestrial vegetation whose debris were consumed by abundant shreddersdominated by the prosobranch Melanopsis praemorsa. The lower course of the Zegzel has sparse riparian vegetation and muchfine detritus, and collectors such as Ecdyonurus rothschildi, Caenis luctuosa, the Diptera Corynoneurinae and Tanytarsini,occurred. In contrast, dry, flowing-, and standing-water periods succeed each other in the Cherraa and terrestrial vegetation oftengrows in its bed. M. praemorsa was replaced by the air-breathing pulmonate Physa acuta, accompanied by the adults and larvaeof flying insects. However many shredders did not develop on the abundant plant litter. The short length of the submersionperiod was probably responsible for this lack of efficiency in the exploitation of such a non-limiting food resource.