Which Belize atoll contains the Great Blue Hole?

The Belize atoll containing the Great Blue Hole is Lighthouse Reef.

The Great Blue Hole lies near the center of Lighthouse Reef, a small atoll about 70 kilometres from Belize City and the Belize mainland. The circular marine sinkhole is approximately 318 metres across and 124 metres deep, making its vivid blue color and near-perfect shape visible from above.

The feature began as a limestone cave system during periods of the Quaternary glaciation, when sea levels were much lower. Stalactites found underwater show that the cave formed in multiple stages, with evidence of formation or exposure around 153,000, 66,000, 60,000, and 15,000 years ago. Rising seas eventually flooded the cave and created the marine sinkhole seen today.

Jacques Cousteau helped make the site famous when his research vessel Calypso visited in 1971 to chart its depths. The Great Blue Hole is part of the Belize Barrier Reef Reserve System, a UNESCO World Heritage Site. A common mix-up is Turneffe Atoll, another major Belizean reef area, but the Great Blue Hole belongs specifically to Lighthouse Reef.