Shark Island

Shark Island sits a few hundred metres to under a kilometre off Koh Tao's southeast tip. Descents typically pass a safety-stop shelf around three to five metres before opening onto the working range: granite boulders, gullies and ridgelines sloping down to sand at fourteen to twenty metres, with sandy patches and rockier ledges at the deeper end pushing the maximum to twenty-eight. Purple soft corals, gorgonian fans and hard coral cover much of the structure, and great barracuda, blue-spotted stingrays, moray eels, hawksbill turtles and nudibranchs are commonly reported on most dives. Open Water divers are guided through the calmer, shallower sections; the fuller circuit into the deeper ledges, where the site's currents are felt most, is why most operators put Advanced Open Water at the door.

The name says nothing about how often a shark actually shows up here. Its origin is not in question: seen from the south or southeast, the islet's exposed rock reads as a shark's dorsal fin cutting the surface, and the site takes its own name and its Thai name, Gong Sai Deang, from that shape alone. Whether the animal turns up is a genuinely open question among the operators who dive it. One operator's own species list skips blacktip reef sharks by name, though the list is not shark-free: it includes whale sharks. Another lists blacktip reef sharks among what divers encounter without saying how often, and a third describes them roaming the surrounding reef, language closer to a resident population than an occasional guest. No survey or sighting count exists anywhere to settle which picture is accurate.

A second, separate draw sits just off the island's south side: the MV Trident, a decommissioned liveaboard scuttled as an artificial reef at around thirty-six metres. It lies well below Shark Island's own recreational range and is dived as its own trip, open only to divers holding deep or wreck certification. Whale sharks add a third, seasonal layer: reported around plankton blooms, but with real disagreement over how often they pass and which months are peak, so an encounter is best treated as a seasonal bonus, not something you can pin to a fixed date.

Currents are the condition called out again and again, running from mild to occasionally strong and unpredictable depending on where you are around the island; ask your guide to work the sheltered lee side if moving water is not what you came for. Titan triggerfish nest on the reef, and one source specifically calls out aggressive, territorial behaviour from them during nesting season: give a nesting fish room and back off if it turns defensive. Boat time to the site varies widely with where your operator departs from. Ask whoever you book through for the current schedule; do not assume a fixed transfer time.