Diving the Great Blue Hole. The Great Blue Hole is over 300 meters across and 124 meters deep, and was formed during several episodes of quaternary glaciation between 150,000 to 15,000 years ago. It lies near the centre of Lighthouse Reef, a small atoll 70 km (43 mi) from the mainland and Belize City. The hole is over over 980ft (300m) across at the rim and the Cambrian Foundation measured the hole’s depth at 406ft (124m) in 1997. When you dive the Blue Hole in Dahab, you have taken on one of the most challenging environments in diving and you will experience something truly remarkable. But thanks to the State of Ohio, The Blue Hole is open again at another, nearby location. Branson has joined a team of scientists, explorers, and filmmakers to discover what lies at the very bottom of the Great Blue Hole in Belize. The Great Blue Hole off the coast of Belize is the world's biggest ocean sinkhole, measuring 1,000 feet across and over 400 feet in depth. The Great Blue Hole is 300 metres (984 feet) in diameter, the largest of known blue holes in the world, and it measures 124 metres (407 feet) in depth. This is why so many divers brave the 80 meter wide hole, despite the fact that many divers have lost their lives here. The great blue hole remains one of the top attractions in Belize. The dive crew at Amigos del Mar Dive Shop, San Pedro, made a strange and unique discovery at the Great Blue Hole on Thursday, August 18, 2011, as Michael Hancock pulled out a deep sea fish that has yet to be identified by personnel at the Hol Chan Marine Reserve office.Michael Hancock, dive master at Amigos del Mar, explains that he discovered the deep black colored fish It was formed during several episodes of quaternary glaciation when sea levels were much lower. When you dive the Blue Hole in Dahab, you have taken on one of the most challenging environments in diving and you will experience something truly remarkable. Photo credit. It closed after nearly 70 years in the 1990's. The Great Blue Hole of Belize Blue Hole is well known as one of the eight wonders of the world. Globe Guide Media Inc /Shutterstock Blue holes like these are essentially oceanic sinkholes formed during the last Ice Age when sea levels were lower. The hole is circular in shape, and is 125 meters deep. The Great Blue Hole is a giant marine sinkhole off the coast of Belize.. In addition, most of the blue-hole bacteria were found to thrive near the halocline—a relatively thin layer where there's some turbulent mixing of freshwater and saltwater. The area is protected from fishing as it is the centerpiece of The Blue Hole Natural Monument Marine Park.