Macroalgal blooms (Green tides) are occurring more frequently in many regions of the world because of the combined effects of increasingly intense human activity and climate change. In the last decade, the world’s largest Ulva prolifera green tide has become a recurrent phenomenon, appearing every summer in the southern Yellow Sea, China, and it is getting worse. Green tides can hurt coastal tourism and eradicate aquaculture and artisanal fishing. Eutrophication in nearshore waters is the ultimate explanation for the explosive growth of the macroalgal biomass, but the specific course of each nearshore green tides is often complex and requires in-depth and extensive research to develop effective mitigation strategies. It is becoming increasingly urgent to prevent and control the bloom at the early stage, promote the ecological virtuous cycle, and efficiently salvage and use these valuable raw materials.