The Great Blue Hole

The Great Blue Hole is a giant underwater sinkhole — a natural marine karst formation — located within Lighthouse Reef Atoll, Belize. It measures over 400 feet (approximately 300 metres) across and reaches a maximum depth of 124 metres (407 feet), making it one of the largest features of its kind in the world.

The interior terrain is defined by its stalactite formations, which descend from the overhangs and cave-like walls as divers drop into the blue. The bottom is cave-type, and the sheer scale of the hole means depth accumulates quickly and without obvious cues — divers can exceed planned depths before realising it. Buoyancy control is critical throughout the dive, and the deep penetration means decompression is required. Nitrogen narcosis is a genuine concern at depth, and the overhangs and stalactites present additional hazards. This site is rated technical difficulty and is not suitable for inexperienced divers.

Marine life at the site includes reef sharks and Caribbean reef sharks gliding through the water column, along with the elusive midnight parrotfish. The surrounding reef supports nurse sharks, stingrays, and tropical fish. Water temperature is 24°C, and visibility is characteristically great inside the hole.