Dean's Blue Hole

Dean's Blue Hole is a perfectly circular vertical shaft of open ocean that drops through the seafloor to a depth of 202 metres, the second deepest blue hole in the world and the deepest with a fully documented underwater cave system, making it one of the most extraordinary natural formations accessible to divers on the planet.

The blue hole opens into a cave system at depth that is considered among the most spectacular underwater caves in the world, with a large chamber that has been explored and mapped by the most accomplished cave divers on earth, reachable only by technical diving with extensive specialized training and equipment.

The blue hole became globally known in 2013 when New Zealand freediver William Trubridge set a world record here, descending to 121 metres on a single breath of air in the Variable Weight freediving category, and the site has hosted annual Vertical Blue freediving competitions that draw the world's best athletes to its uniquely clear and still waters.

For snorkellers and recreational divers the experience is equally compelling; the opening of the blue hole is accessible through a narrow channel on its western edge, with a maximum depth of about 20 metres at the lip, and inside the hole the water is famously clear with excellent visibility even at depth, though the drop-off begins immediately just a few metres from the edge.

One of the most remarkable underwater phenomena at Dean's Blue Hole is the halocline, a visible layer where fresh water from underground springs meets the salt water of the open ocean, creating a shimmering distortion effect that looks like a sheet of glass suspended in the water column and is unlike anything found at most diving destinations.

The marine life in and around the blue hole includes nurse sharks, groupers, tarpon and jacks that patrol the walls, and the surrounding coastal area of Long Island is relatively undeveloped, with dry coastal scrub and cliffs providing a dramatic above-water counterpart to the underwater drama below.

Blue holes are marine sinkholes formed during glacial periods when sea levels were much lower, with the Bahamas blue holes being among the most studied in the world due to their accessibility and exceptional preservation of geological and archaeological records including ancient stalactites, extinct dinosaur figures and even human artefacts.

The surrounding Long Island coastline is equally compelling above water, with dramatic grey limestone cliffs, secluded coves and the scattered ruins of colonial-era plantation buildings that recall the harsh history of the salt and sisal industries that once dominated this island's economy.

The second deepest blue hole in the world with a fully explored cave system, unique on the planet.

The site of multiple freediving world records and annual competitions, making it a legendary destination in the freediving world.

The halocline phenomenon creates a visually surreal underwater environment found at very few sites globally.