Abstract: Estuaries renewable energy, salinity gradient energy (SGE) as example, can be gained from the controlled mixing of two solutions with different salt concentrations, taking advantage of the chemical potential difference. This energy promises to assist in the effort to reduce carbon emissions worldwide. Two main technology types, Reverse Electro-Dialysis (RED) and Pressure-Retarded Osmosis (PRO), make use of semi-permeable membranes which generate an osmotic potential that can be used to generate electricity using turbines in deltas, estuaries, fjords or hyper-saline lakes. In PRO, semi-permeable membranes placed between the two streams of solutions allow the transport of water from low pressure diluted solution to high-pressure concentrated solution. RED requires two alternating semi-permeable membranes that allow the diffusion of the ions but not the flow of H2O. As we know that the estuaries are among the most biologically productive ecosystems on the planet critical to the life cycles of fish, other aquatic animals and the creatures which feed on them. Recently the wider estuarine community asks if this energy could have significant effects on the fisheries and marine life caused by the diverted flow. In this presentation, we focus on the degree of the impact of estuary energy on environment and ecology.