CHINA

In Depth: Why ‘Green Tides’ Keep Rolling Into East China

Published: Sep. 5, 2025 7:03 a.m. GMT+8

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Part of the First Beach in Qingdao is covered with algae on July 23. Photo: Kang Jia/Caixin

At noon on July 9, the temperature on Dujiadao Island in East China’s Shandong province was around 34 degrees Celsius (93 F). As the tide came in, vast sheets of algae called Ulva prolifera rolled ashore like an enormous quilt. Layer upon layer of algae piled up on the shore, creating a green blanket as thick as a person’s forearm.

Local resident Pan Fei moved quickly to stop the green tide from smothering his aquaculture ponds. He hired villagers to haul out the algae with long nets under the blazing sun, but the algae returned as soon as the tide rolled back in, filling his ponds.

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What Happened When

2006 to 2010：: China Marine Ecological Environment Bulletin reported most waters at the Yangtze estuary, northern Jiangsu shoals, and Hangzhou Bay fell below Class IV standards due to excessive nutrients.

2008：: Green-tide algae first became a national issue during the Beijing Olympics, when Qingdao hosted the sailing events and a major algae bloom necessitated an emergency cleanup operation.

2009：: Qingdao Seawin Biotech Group Co. Ltd. began processing Ulva into fertilizer and feed additives.

2016：: In Qingdao, aquaculture losses from an algae bloom reached 4.8 billion yuan. China issued a Yellow Sea control plan; Jiangsu began regulating laver farms and banning attached algae dumping.

In the 12 years before 2019：: Blooms covering more than 50,000 square kilometers struck five times.

2019：: China’s natural resources ministry and the Jiangsu provincial government ordered that seaweed farming along Jiangsu’s northern shoals be cut by nearly two-thirds to curb green tides.

2020：: Due to the enforcement of restrictions on seaweed farming, the Yellow Sea bloom shrank to its smallest in a decade, at 18,200 square kilometers.

2021：: The Yellow Sea green tide reached a record size of 61,900 square kilometers, the largest ever recorded worldwide.

2022：: Qingdao deployed 13,400 vessels for coastal algae cleanup at a cost of 305 million yuan.

2023：: Qingdao recorded algae clinging to laver rafts down 98.5% from 2019 levels, but the bloom was nearly as large as in the record year 2021.

2023：: Publication of the Ministry of Natural Resources’ China Marine Disaster Bulletin, citing the 2020 bloom size.

2024：: Weihai’s tourism revenue reached 70 billion yuan (18.8% of GDP), Yantai’s 113.9 billion yuan (18.8% of GDP), affected partly by algae blooms. Jiangsu province’s top political advisory body proposed tackling nitrogen and phosphorus pollution to address algae blooms, which have persisted in the Yellow Sea for 19 years since 2006. The area used for laver cultivation in Jiangsu fell from 115,316 acres to 50,755 acres since 2016.

In the 6 years from 2019 to 2025：: Blooms larger than 50,000 square kilometers occurred four times, according to the Jiangsu Marine Fisheries Research Institute.

Early June 2025：: Pan Fei stocked his ponds with 100,000 yuan worth of sea cucumber seedlings, only to be severely impacted by subsequent algae blooms.

Mid-May 2025 to late July 2025：: Qingdao budgeted 84.8 million yuan for algae cleanup contracts.

Early July 2025：: Rushan Silver Beach turned green overnight due to algae; many tourists left after two to three days of foul odor.

Noon on July 9, 2025：: The temperature on Dujiadao Island was about 34°C as a large green tide of Ulva prolifera algae washed ashore, heavily impacting local aquaculture.