Salinity gradient energy is a clean source of renewable energy, which can be harnessed from a region where fresh river water connects to a hypersaline sea or lake. The funnel shaped Hooghly Estuarine river system connects to comparatively more saline Bay of Bengal. This change in salinity can be used to extract salinity gradient energy. Here, analyses has been done on the energy potential due to salinity gradient for the Hooghly estuarine system using Reverse Electrodialysis (RED) process to estimate the available energy. Using the available data for solving the required thermodynamic equations, theoretical potential as high as 1425.3 MW and low as 228.4 MW was calculated for the River Estuarine during May and November. The study also explains the effect of the monsoon season in the extractable energy. The viability of any such energy extraction project depends on the sale price of the generated power and membrane efficiency. A number of laboratory experiments in the previous studies were done, which state the energy efficiency of RED process to be 33-44 % considering equal volume of seawater and river water. The calculated values are based on recently available membranes and better results can be anticipated with the use of advanced membrane.