Southwest Pinnacle: Dive Site, Koh Tao's Underwater Mountain Range

Southwest Pinnacle is a group of submerged granite peaks in open water south-west of Koh Tao. Divers often call it an underwater mountain range: the rocks climb from sand at around 30 m to a summit just 5 to 6 m below the surface, and they are classically counted as seven.

For a Southwest Pinnacle dive on Koh Tao, plan on a boat ride of about 40 to 45 minutes (an hour on a slow day). It is rated Advanced, it is a big-fish site, and it is one of the best multi-level dives around the island.

Southwest Pinnacle dive site map

1. 1Main shallow pinnacle, top 5 m
2. 2North ridge pinnacles
3. 3East ridge pinnacles
4. 4South ridge pinnacles
5. 5West pinnacles, giant groupers
6. 6Secret pinnacle, guided only

Diving Southwest Pinnacle: the route

The staggered heights of the rocks make the profile easy to plan. Start deep around the bases at 22 to 28 m, work up the ridges, and finish on the shallowest summit at about 5 to 6 m for your safety stop. It is a natural way to use your air and no-stop time well.

Because the rocks stand at different heights, the dive feels like a walk through a mountain range rather than a lap around one rock. You move through corridors between the pinnacles, with the big groupers sitting on the western side and the schooling fish moving above you in the blue. Take your time on the way up. The shallow pinnacle is a lovely place to hang for the last few minutes, with anemones, pink anemonefish and yellow boxfish around you.

It is a deep-adventure and Deep Diver favourite, and many guides also use it for nitrox and sidemount dives because the staggered profile gives you so many levels to work with.

Underwater layout

The formation is a multi-peaked granite ridge system, with staggered pinnacles that form natural corridors. The main summit reaches to about 5 to 6 m. The pinnacle bases sit at roughly 22 to 28 m, and the sand beyond is at about 30 m. Guides do not all agree on the exact number or position of the peaks, so expect your briefing to differ a little from this page.

Sea whips, black coral and barrel sponges colonise the deeper bases, and the layered rock and crevices hold shrimp and rays. The deeper western side is where giant groupers like to sit.

Some guides also look for a smaller secret pinnacle out in the blue, a 5 to 10 minute swim from the main formation. It needs good visibility and a guide who knows the bearing.

Marine life at Southwest Pinnacle

Giant groupers are the stars. They patrol the rock and tolerate divers, and batfish like to tag along. Overhead, fusiliers stream past while trevally and barracuda hunt through them.

• Shallow pinnacle: anemones with pink anemonefish and yellow boxfish.
• Residents: chevron barracuda, titan triggerfish and white-eyed morays.
• Seasonal and occasional: whale sharks, guitar sharks, eagle rays, cuttlefish and cobia.
• Macro: boxer and cleaner shrimps, blue-spotted ribbontail rays under ledges and nudibranchs.

Whale sharks drift through in season, though never on demand.

Look in the cracks as well as out in the blue. Shrimp hide in the layered rock, and rays rest under the ledges. Torch in hand, a slow pass along a ridge often turns up more than a fast lap of the whole site.

Conditions and best time to dive

Current ranges from slight to moderate at certain times of the month, and it can build to strong. Visibility is typically 15 to 30 m in good conditions, but can drop well below that on a bad day. The site is dived through much of the year, with March to October often mentioned as the best stretch and April to September the peak. Rough weather can cancel offshore trips.

Tips from local divers

• Plan a multi-level profile and use the shallow summit for the safety stop.
• Shine a torch into crevices for shrimp.
• Nitrox or sidemount helps with bottom time on the deeper bases.
• Pay attention to the briefing about triggerfish. They can be aggressive when nesting.
• Only try for the secret pinnacle in good visibility with a guide who knows it.

Safety notes

Depth goes to about 30 m, and currents can build quickly. Titan triggerfish are territorial when nesting, and the anemone tentacles on the shallow pinnacle can sting. Poor visibility makes navigating to the secret pinnacle risky. Open Water divers are usually kept to the shallow summit, and most operators rate the site Advanced.

Brief your buddy on the plan before you get in: where the shallow summit is, what your turn pressure is, and what to do if the current picks up. On a site with this much going on, it is easy to lose track of depth and gas.

Why dive Southwest Pinnacle

• Giant groupers that ignore divers
• Shallow summit at 5 to 6 m for the safety stop
• Fusiliers, barracuda, trevally and batfish
• Whale sharks in season
• Anemone-covered main pinnacle with boxfish
• Secret pinnacle on good-visibility days

Southwest Pinnacle: frequently asked questions

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