Southwest Pinnacle

The dive follows a circuit: divers typically drop onto the main cluster of granite peaks and work around it before crossing open sand channels to a set of outlying rocks a fin kick or two away. The shallowest peaks break the surface zone at 5 to 7 metres, and the group threads down through several distinct levels toward a sandy base; the top of the main formation, carpeted in sea anemones, is a favourite spot to finish a dive as air runs low. One operator running trips here describes the site as beautifully exposed, and that exposure is what pulls the current through and the fish with it: expect schools of yellowtail barracuda, snapper and both big-eye and giant trevally working the open water off the rock, plus longfin batfish holding station in the lee of the formation. A detached rock known locally as the secret pinnacle sits a short swim from the main group, worth the extra air and bottom time if there is gas left for it. Resident titan triggerfish patrol their patch of reef and can turn territorial when nesting; a calm, unhurried approach and a clear dive briefing keep the encounter easy.

Southwest Pinnacle is one of two boat-only offshore pinnacles that anchor Koh Tao's day-trip diving for certified divers, its partner being Chumphon Pinnacle to the north. What sets it apart is the combination: dense schooling fish over open water, an anemone field thick enough to carpet the entire top of the main rock, and consistently good odds of a whale shark, best in March to May and again in October and November, when a juvenile has been known to stay long enough for two full dives with it. The granite forms several distinct peaks in a rough ring, with the current sweeping between them bringing in large resident groupers unfazed by passing divers. One operator schedules the site into a three-stop rotation with Chumphon Pinnacle and Sail Rock, running all three as a single offshore circuit over consecutive days.

Nitrox is worth arranging before the day, especially for divers planning the swim out to the secret pinnacle, where the extra bottom time pays off. Boats leave early, typically 07:20 to 07:30, both to catch the reef at its most active and to reach the site ahead of the rest of the fleet; return is usually by early afternoon. Being genuinely offshore, the trip is more weather-dependent than Koh Tao's inshore sites, and a rough crossing can be the harder part of the day. Open Water divers are typically guided along the shallower sections to about 18 metres; Advanced Open Water suits the full depth and current range, and some operators ask for at least 20 to 30 logged dives before taking it on. In March 2025, a dive boat bound for the site caught fire roughly six nautical miles offshore, and one passenger died. It was an isolated incident on a single boat, and nothing about diving the site itself has been linked to it.12