The expansion of seawater desalination is presented as a new way to supply fresh water for many coastal regions as an effort to counteract the increasing water scarcity. However, brine discharges also pose significant environmental challenges regarding their potential environmental impacts of marine ecosystems. The main objective of this study was to assess the physico-chemical impact of the brine discharges from Seawater Reverse Osmosis (SWRO) desalination plants on South America pacific coastal ecosystems, assessing its potential physicalchemical impact (temperature, salinity, density and dissolved oxygen) on the receiving marine environment, and evaluating the oxidative and osmotic stress responses of the red macroalgae Rhodymenia corallina through diagnostic biomarkers in field-transplantation experiments. Our results showed that the increase over natural salinity in the affected area was less than 3.5 % in a radius of 50 m from the discharge point. Also, we demonstrated that the brine discharges increase the density but not significant affect the temperature and dis- solved oxygen of the marine environment. In addition, diagnostic biomarkers showed a negative effect on oxidative, osmotic and antioxidant stress responses in R. corallina after two days of brine exposure, particularly at the nearest brine diffuser transplantation site. However, after five days, antioxidant and osmotic parameters exhibited full recovery, indicating the cessation of the redox imbalance. Based on the results obtained, we demonstrated that the use of appropriate mitigation measures combined with an appropriate oceanographic location of the submarine outfall, would ensure a sustainable desalination operation without generating sig- nificant environmental impacts on the coastal ecosystems.