Diving the Great Blue Hole

The Great Blue Hole is a vast underwater sinkhole located off the coast of Belize. It sits close to the middle of Lighthouse Reef, a small atoll roughly 70 kilometers from mainland Belize and Belize City. Almost perfectly circular, the formation measures more than 300 meters in diameter and reaches a depth of about 125 meters.

Evidence of an Ancient Past

Although the Blue Hole is now filled with marine life, its vertical cavern also preserves geological evidence from a time when it was exposed above sea level. During periods when large quantities of the planet’s water were locked away in glaciers, global sea levels dropped significantly. Under those conditions, stalactites, also known as dripstones, developed within the cave. Many of these formations remain intact beneath the water today.

A Famous Diving Destination

The mysterious Blue Hole gained international attention when Jacques Cousteau introduced it to millions of television viewers in 1971 through The Undersea World of Jacques-Yves Cousteau. In the present day, diving vessels retrace the route made famous by the Calypso, bringing visitors to one of the world’s most renowned scuba-diving locations.

Part of Belize’s World Heritage Site

The Blue Hole Natural Monument is recognized as one of the seven wonders within Belize’s World Heritage Site. The Belize Barrier Reef Reserve System covers approximately 963 square kilometers and provides a remarkable example of reef formations, including fringing reefs, barrier reefs, and atolls.

A Remarkable Coastal Ecosystem

Belize’s coastal region forms an exceptional natural environment. It includes the largest barrier reef in the Northern Hemisphere, offshore atolls, hundreds of sandy cays, mangrove forests, coastal lagoons, and estuaries. Its seven protected sites demonstrate different stages in the evolution of reef formation while also providing important habitats for numerous threatened species.

The Belize Barrier Reef

The reef stretches from the Mexican border in the north toward the vicinity of the Guatemalan border in the south. Belize’s submarine shelf and barrier reef together form part of the world’s second-largest reef system and the largest reef complex in the Atlantic-Caribbean region. Beyond the main barrier are three major atolls: Turneffe Islands, Lighthouse Reef, and Glover’s Reef.

The Offshore Lagoon

A broad offshore lagoon lies between the mainland and the barrier reef. Moving from north to south, both its width and depth increase. In the northern section, the water is generally only 2–3 meters deep and covers a flat, largely featureless seabed extending approximately 20–25 kilometers across. Farther south, beyond Belize City, the continental shelf gradually becomes deeper, creating a channel between the mainland and the outer platform. In the Gulf of Honduras, this channel reaches depths of around 65 meters.

Sand and Mangrove Cays

Around 450 sand and mangrove cays are scattered within the barrier reef and surrounding atolls. Their sizes vary greatly, ranging from temporary sand spits to substantial permanent islands that can support human communities. Ambergris Caye is the largest of these islands and is home to the village of San Pedro as well as Portofino Beach Resort Belize. Several PADI-certified diving operators travel to Half Moon Caye Natural Monument from San Pedro, Caye Caulker, and Belize City.

Marine Life and Scuba Diving

The Great Blue Hole attracts recreational divers from around the world because of its exceptionally clear water and diverse marine life. Divers may encounter giant groupers, nurse sharks, and several reef shark species, including Caribbean reef sharks and blacktip sharks. Bull sharks and hammerheads have also been reported in the area, although they are not commonly seen.

Most excursions to the Great Blue Hole take an entire day. A typical diving trip includes one descent into the Blue Hole followed by two additional dives at nearby reef sites, allowing visitors to experience both the dramatic underwater cavern and the surrounding coral ecosystem.