Every summer since 2007, algal blooms have grown in China's Yellow Sea (1). This year, covering about 1746 km2, the bloom is 2.3 times larger than the country's previous record-holding bloom in 2013 (2). Such massive quantities of algae block sunlight from entering the ocean and deplete oxygen levels, suffocating marine life (3). The algae also pose challenges for tourism and marine transport. The city of Qingdao has deployed 12,686 boats to clean the water, collecting 457,700 tons of algae by 12 July (2). The algae are expected to persist until mid-August (4), at enormous economic and biological cost. Mitigating the damage will require regional collaboration.