Aquatic crustaceans have a cosmopolitan distribution; despite their great importance in aquatic ecosystems, literature on this group is relatively scarce, especially in the Merja of Fouarat. Therefore, in the present article, a contribution was made to enrich the data on this group. The results show the existence of 34 species, divided into five families, all belonging to a single superorder of Diplostraca. Furthermore, these results show that the distribution of the different species is not homogeneous and that the species Daphnia pulex, Daphnia magna, Megafenestra aurita, Simocephalus expinosus, Alona elegans elegans, Alona pulchella, Alona rectangula, Chydorus sphaericus, Dunhevedia crassa, Pleuroxus letourneuxi, Macrothrix hirsuticornis, and Macrothrix laticornis, are ubiquitous species that can be found at sites with temporary, semi-temporary to permanent impoundment. While, the species Ceriodaphnia dubia, Ceriodaphnia quadrangulata, Daphnia atkinsoni, Daphnia chevreuvi, Daphnia similis, Scapholeberis kingi, Simocephalus vetelus, Alona affinis, Alona elegans lebes, Alona esteparica, Biapertura karua, Ephermeroporus phintonicus, Leydigia ciliata, Tretocephala ambigua, E chinsca rosea, and Moina brachiata are strictly confined to sites with temporary impoundment. However, the species Ceriodaphnia reticulata, Acroperus harpae, Alona costata, Eurycercus lamellatus, Graptoleberis testudinaria, Moina micrura, and Moina salina are restricted to sites with semi-permanent to permanent flooding.