'World's deepest' underwater sinkhole found in China

Scientists have discovered what's being described as the world's deepest underwater sinkhole in the South China Sea, China's state broadcaster CCTV reported. Called the "Dragon Hole" by locals, it's 987 feet (300 meters) deep, according to researchers who have spent the past year exploring the site. Scientists from the Sansha Ship Course Research Institute for Coral Protection used an underwater robot with a depth sensor to determine the size of the sinkhole. Researchers found more than 20 species of fish in the upper part of the sinkhole, which is also known as a blue hole. But below 100 meters, it is largely oxygen-free, meaning life is unlikely to survive there. A "blue hole" is a large sinkhole or cave system in the ocean that is visible from the surface. Described by locals as the "eye" of the South China Sea, the hole is located in a coral reef off the Paracel Islands. Related: Has South China Sea ruling set scene for next global conflict? Dean's Blue Hole in the Bahamas was previously thought to be the world's deepest underwater sinkhole, at a depth of more than 660 feet. The Sansha city government in Hainan Province, China, said it has drafted measures to protect and study the blue hole in the South China Sea.