Reported cases of coastal hypoxia or low oxygen areas have doubled in each of the last four decades, threatening global environment benefits in most of the Large Marine Ecosystems (LMEs) in which GEF supports programs. GEF requested STAP to review the scientific evidence on coastal hypoxia and advise how to address the issue, beyond current actions. STAP concludes that the growing problem of coastal hypoxia requires accelerated GEF attention. Hypoxia is caused by eutrophication, i.e., the overloading of waters with nutrients, especially nitrogen, phosphorous and silicon and/or organic matter. Coastal areas are suffering from accelerating nutrient pollution from multiple sources including agriculture and livestock production, sewage and industrial waste, plus additional complex temperature and water exchange impacts from climate change. Nutrient effects on water oxygen levels are exacerbated when local water bodies become stratified and mixing, and thus oxygenation, of layers is prevented.