Huangyan dao: China has discovered a new "blue hole" formed by a coral reef near Huangyan Dao (Scarborough Shoal) in the South China Sea. This is the first blue hole from a coral reef to be explored and investigated in the country.

According to Thai News Agency, intensive research and exploration through deep-sea diving, remotely operated underwater vehicles (ROVs), and aerial mapping have revealed that this blue hole covers an area of approximately 1,491.7 square meters, with a maximum diameter of 56.3 meters. Its exterior is almost perfectly circular, and it is 16.6 meters deep. The interior has a conical structure with a narrow bottom. Studies estimate that this hole was formed at least 3,200 years ago through the long-term growth of coral, unlike most blue holes in the world which were originally terrestrial caves during the Ice Age.

Although typical underwater blue holes often lack oxygen and life at deeper levels, this particular hole boasts a rich ecosystem. As many as 165 species of hard corals have been found growing along the holes' walls, along with 184 species of coral fish. It also serves as a habitat for giant clams, sea gypsum, sponges, and sea anemones, and is a crucial refuge and nursery ground for green sea turtles, a top-level protected species in China.

Scientists describe the blue hole as a "time capsule" because its isolated and undisturbed underwater sediment and chemistry allow researchers to analyze past changes in global temperature and environment, trace fluctuations in regional sea levels, and understand the mechanisms of adaptation and recovery in marine ecosystems.

The area was declared the Huangyan Island National Nature Reserve in September 2025 to enhance proactive conservation and long-term research. However, the Scarborough Shoal remains a significant overlapping and disputed maritime area between China and the Philippines.