The present state of knowledge of the Pakistani fresh water arthropod (Crustacea, Insecta and Arachnida) fauna is discussed. It is noted that running waters are highly heterogeneous ecosystems with constant and gradual changes in conditions, such as their width, depth, temperature, and flow. Realizing the fact that aquatic invertebrates particularly the arthropods can be used as natural indicators in lotic habit and habitats as well as in lentic environments we selected this group for report writing.