"Blue holes" are mystifying to look at, the large, deep pits appearing a shade of blue that's just as deep and in stark contrast to the shallow waters around them. And what we've long considered the planet's deepest—the 663-foot Dean's Blue Hole in the Bahamas—has been relegated to second place, say Chinese researchers. They announced Friday that 11 months of study have confirmed that an underwater sinkhole in the South China Sea crushes that record. At 987 feet, it could nearly swallow the Eiffel Tower, reports the Washington Post. Known colloquially as "Dragon Hole" and the "eye " of the South China Sea, the depth was confirmed using a VideoRay Pro 4 underwater robot equipped with a depth sensor, reports Xinhua.
The researchers further found that oxygen exists only in the top third of the blue hole, and they identified more than 20 fish and marine species in that top layer. The local government has drafted measures related to the protection and study of the hole. In its report on the discovery, Kyodo notes that when it's humans, not robots, exploring these blue holes, the situation is "extremely dangerous." On Nov. 17, 2013, a 32-year-old free-diver from Brooklyn drowned at Dean’s Blue Hole. The Economist ranks free-diving—relying on a single breath to dive as deep as you can —as second only to BASE-jumping in terms of its danger level. "Diving at extreme depths brutalizes the lungs, which at a depth of [100 feet] compress to a quarter of their normal size." (This blue hole in Belize may hold the secret to the Mayan collapse.)