Dam construction, channelization and diversion of water disrupt natural biological cycles of aquatic species viz. seasonal migration of fish & various insects with aquatic larval stage and other aquatic species as well as ethnic fauna of various riparian plant species. The denial of migration may result into permanent and irreversible reduction of fish stocks ranging from lower level of abundance to complete extermination. The niche so vacated will be later filled by coarse & undesirable species. Considerable reduction of flow in the residual various tailing below the dam may completely dry up the fish spawning/breeding grounds, shallow areas are formed which impede fish movements.