Lighthouse Reef is an atoll lying 35 miles (55 km) east of the huge Belize barrier reef, off the coast of central Belize. It is roughly oval-shaped, about 23 miles (38 km) long, and 5 miles (8 km) wide on average. Like all atolls, it is bounded by a ring-like outer structure of coral formations, many of which break the surface.
These form a natural barrier against the sea and surround a lagoon, which sits on top of a mass of limestone. The lagoon is relatively deep but contains numerous patch reefs along with six small, sandy, low-lying islands, or cays (one containing a dive center). At its center is Lighthouse Reef’s most remarkable feature—a large, almost circular sinkhole in the limestone, known as the Great Blue Hole.
Approximately 480 ft (145 m) deep, this feature formed some 18,000 years ago during the last ice age, when much of Lighthouse Reef was above sea level. At that time, freshwater erosion produced a complex of air-filled caves and tunnels in the limestone. At some point, the ceiling of one of the caves collapsed, producing what is now the entrance to the Blue Hole. Later, as sea level rose, the cave complex flooded, and it is now accessible only by adventurous scuba divers.
Apart from the Blue Hole, the atoll boasts large areas of healthy, abundant, mainly unexplored coral formations. As well as patch reefs within the atoll, around its margins are many spectacular coral-encrusted walls (dropoffs) that descend to depths of several hundred yards. Lighthouse Reef exhibits a biological diversity typical of the region; it is home to some 200 fish species and 60 species of stony corals.
Diving the great blue hole
The Great Blue Hole is one of the world’s most exciting dive sites. It is not recommended for the fainthearted (as sharks are commonly encountered) or for novice divers (because perfect buoyancy control is needed). At 125 ft (38 m) depth, an array of impressive ancient stalactites can be seen hanging from the slanting walls of the hole. The entrance to a system of caves and tunnels lies a few yards farther down.