<p>The co-discharge of brine and cooling water is widely regarded as a preferred method for desalination brine disposal. However, existing research on the effectiveness of this approach primarily relies on software simulations, with limited studies addressing its impact in real marine environments. This study conducted a field investigation to evaluate the effects of co-discharge of brine and cooling water on water quality, plankton, and macrobenthic organisms in the receiving marine ecosystem. Two discharge scenarios were examined: a low mixing ratio (brine comprising 10% of the total discharge volume) and a high mixing ratio (brine comprising 50% of the total discharge volume). The results demonstrated that the combined discharge of brine and cooling water influences not only temperature and salinity but also other water quality parameters. Mixing ratios significantly affected pH, water temperature, salinity, and aluminum (Al) concentrations in the receiving waters. In the high mixing ratio discharge area, pH and salinity increased by 2.4% and 3.1%, respectively, whereas temperature and Al concentration decreased by 5.1% and 43.8%, respectively. Phytoplankton abundance and species number decreased by 90% and 50%, respectively, near the low mixing ratio outlet, but increased by 96% and 28%, respectively, near the high mixing ratio outlet. In contrast, no obvious differences were observed in zooplankton species composition, abundance, or diversity index between the two discharge areas. The findings of this study provide new insights into the selection of discharge methods and brine discharge management.</p>