This study addresses the impact of hypersaline discharge from seawater reverse osmosis (SWRO) plants on recipient marine ecosystems. The primary outputs and outcomes are to measure the environmental tolerances of key species, develop biomarker tools relevant to these species, and to develop risk assessment and mitigation strategies relevant to the release of desalination waste brine into the receiving environment. The seagrass component consists of examining a range of responses of a target seagrass Posidonia australis to increased salinity and brine in a series of mesocosms experiments, carried out at UWA and an extensive field survey of nearshore environments along some 70 km of Geographe Bay, centred around a major desalination plant (SSDP) near Binningup.