eDNA is a new promising tool for the surveillance of species biodiversity and represents a source of information for extracting knowledge about past and present biological diversity. Although, only few study gave been conducted to collect, separate and interpret the DNA application, still this tool is quite helpful in improving the conservation and management. It has revealed the ancient terrestrial system and organisms. This is a literature review to assess information regarding the origin, sustenance and degradation of eDNA in an aquatic system. However eDNA application are mainly imparted on terrestrial animals, aquatic system is not much explored. The approach in aquatic system is found marred and biases regarding the DNA behaviour and its degradation Environmental scenario, contamination is common and reference database is in complete. This chapter comprises about look on the origin, evolution, methodology and application.