China has discovered its first naturally formed coral-reef growth-structure blue hole in the waters of Huangyan Dao. This is the second marine blue hole found in waters under China's jurisdiction, after the Yongle Blue Hole of Sansha, and the first of coral-reef origin.
The blue hole is located in the lagoon of Huangyan Dao. It was identified in August 2025 during an on-site ecological survey led by the South China Institute of Environmental Sciences of the Ministry of Ecology and Environment, together with institutions including the Guangxi Laboratory on the Study of Coral Reefs in the South China Sea of Guangxi University. The entrance area is approximately 1,491.7 square meters, with a maximum diameter of 56.3 meters and a depth of 16.6 meters. Its internal structure is funnel-shaped with a narrow bottom, and turbidity stratification is present inside. Preliminary radiocarbon-14 isotope dating suggests the blue hole formed at least 3,200 years ago.
The blue hole and surrounding waters are rich in biodiversity. Typical coral-reef organisms such as corals, giant clams, fish, sponges and sea anemones are distributed inside. Green sea turtles, a Class I nationally protected wild animal, have been observed resting inside and near the entrance. Successive surveys over two years have recorded 165 species of reef-building corals and 184 species of fish in adjacent waters, and environmental DNA technology has detected over 2,700 marine species. The survey results reflect the positive outcomes of ecological protection in the Huangyan Dao area. In September 2025, the Chinese government established the Huangyan Dao National Nature Reserve.
Going forward, relevant research institutions will further focus on the blue hole's formation mechanisms, ecological and environmental evolution, ecosystem functions, and its contribution to the high biodiversity of Huangyan Dao. More in-depth investigations will be conducted to provide scientific support for strengthened protection of ecosystems and biodiversity in the South China Sea.