India is one of the leading nations in the world in the abundance of inland water resources. Reservoirs constitute the single largest inland fishery resource, both in terms of resource size and productive potential. Reservoirs in Kerala are situated in unique geo-climatic conditions. Reservoirs are human engineered habitats that occur in almost all major river basins in India. When the rivers are impounded, qualitative and quantitative changes in their biota are bound to occur. Effect of such changes in the physico-chemical environment, fish diversity and fish yield are significant in order to plan suitable management programmes on reservoir fisheries.