The Belize Barrier Reef is the longest barrier reef in the western hemisphere and holds the astonishing Great Blue Hole : a vast, perfectly round underwater sinkhole – 300 metres across, 125 metres deep.

It was formed as a limestone cave system during the last glacial period when sea levels were much lower. As the ocean began to rise again, the caves flooded, and the roof collapsed.

Belize Barrier Reef   © Sooboth

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