Shark Island Dive Site, Koh Tao: Depth & Marine Life

Shark Island is one of the most colourful dive sites in Koh Tao, and the name is a bit of a trick. It comes from the rock above the water, which looks like a shark's dorsal fin, not from sharks. This small, uninhabited granite islet sits about 300 m off the south-east tip of the island, a short boat ride from Mae Haad or Sairee.

Under the surface, big granite boulders form slopes, gullies and corridors covered in purple soft corals, gorgonian fans and barrel sponges. Most of the dive happens between 10 and 18 m, so it feels generous without being deep. The catch is the current, which is why many guides treat it as a site for confident divers.

Shark Island dive site map

1Shark Island, fin above water
2Boulders and gullies, to 18 m
3Shallow coral gardens, 4 to 12 m
4Outlying rocks
5Sand slope to 25 to 28 m
6MV Trident wreck, 36 m

Usual route: Drop in on one side of the islet, follow the boulders at 10 to 18 m with the current, check overhangs for rays, and finish in the shallows at the rocks. Drawing based on local dive briefings: approximate, not to scale and not for navigation. Your guide's briefing on the day always comes first.

Diving Shark Island: the route

Boat rides to Shark Island are short, and you tend to see the fin of rock long before you reach it. Your guide will pick the side based on the current that morning, which is part of what makes each dive here a little different.

You can circle the whole islet, but it takes good air consumption, so most operators dive one side per trip. The usual plan is to drop in on one side, follow the boulders at 10 to 18 m with the current, and check the overhangs for rays as you go.

Finish in the shallows around the rocks and do your safety stop at about 5 m. The average dive depth is around 14 m, which gives you a long, relaxed bottom time when the water is kind.

Underwater layout

The islet is made of large granite boulders, some rising more than 10 m above the surface and reaching about 15 m below it. Outlying rocks sit beyond the main islet. One side has shallower coral gardens and the other has deeper boulder areas with overhangs and crevices.

Boulders run from the surface to around 15 to 18 m, and then the bottom turns to sand. That sand slopes down to roughly 25 to 28 m at the south-east end, which is the deepest part of the site. The Trident wreck lies further off in that direction, but it is not part of the normal dive.

Marine life at Shark Island

Shark Island is a good example of why the east side is worth the trip. The granite is covered in life from top to bottom, so even the shallow part of the dive keeps you busy. Slow down and look into the gullies, because that is where the small stuff hides.

This is a site for variety. Yellowtail barracuda and batfish follow divers around, blue-spotted ribbontail rays rest under the overhangs, and titan triggerfish guard patches of reef, so give them space. Turtles are regular visitors and are often the highlight of the dive.

Common: yellowtail barracuda, batfish, titan triggerfish, blackcap butterflyfish, damselfish, moray eels, harlequin sweetlips, scribbled filefish and anemones.
Now and then: eagle rays and whale sharks are occasionally recorded. A leopard shark or blacktip reef shark is reported from time to time, but do not count on it.
Macro: nudibranchs and wart slugs on the corals and boulders.

Conditions and best time to dive

The island is exposed, so currents can be strong, and on rough days the boat may move the dive to another site. Visibility ranges widely, from about 2 m on a bad day to 30 m on a great one, and 10 to 20 m is typical.

We do not have a reliable best month for Shark Island, so check with your dive centre for the week you are here. The shelter on the lee side of the islet can make a big difference to comfort.

Tips from local divers

Explore one side per dive. The site is bigger than it looks.
Bring a wide-angle lens if you shoot photos, the fans and soft corals suit it.
Listen closely to the current briefing and ask where the lee side is.
Snorkelling is sometimes possible in calm conditions, but it is mostly a boat dive.

Safety notes

Watch for strong current, boat traffic around the islet, and depths to 25 to 28 m on the sandy side. Circling the entire island burns air fast, so keep an eye on your gauge. The site is used for deep training and fish ID dives rather than standard Open Water courses, and guides will tell you on the day whether the conditions suit your level.