Above the water, the Similan Islands boast stunning topography, with lush vegetation giving way to granite boulders or white sandy beaches, all surrounded by crystal-clear water. However, it is the underwater scenery that makes the Similans and Surin Islands some of the top scuba diving liveaboard destinations in Thailand and Asia.
Similan Islands
The above-water scenery boasts stunning white sandy beaches with small forested areas. Dive sites include Boulder City, Shark Fin Reef, Anita's Reef, and Three Trees. Underwater, you may encounter leopard (zebra) sharks, blue-spotted stingrays, clown triggerfish, rabbitfish, scorpionfish, snappers, emperor fish, giant trevally, and angelfish. The coral gardens, bommies, and boulder formations are wonderful to explore. Elephant Head Rock, visible from the surface, is the largest pinnacle in the Similans, featuring fantastic swim-throughs. White tip reef sharks, batfish, trevally, and barracuda can often be seen around the boulders. In the cracks and rubble, you might spot smashing mantis shrimp, porcelain crabs, moray eels, and cleaner shrimp. Other sites dominated by huge granite boulders, such as Deep Six, Christmas Point, and North Point, offer sightings of white tip reef sharks, schooling giant trevally, and schools of neon fusiliers.
Koh Bon
This location is the most likely spot to see manta rays on this itinerary. You may also see Napoleon wrasse, sweetlips, octopus, bluefin trevally, giant moray eels, great barracudas, fire dart goby, spiny lobster, and various nudibranchs. Dive sites vary from wall diving to gently sloping reefs, and from submerged boulders to coral gardens. Diving on the West Ridge can be an adrenaline-filled drift with amazing views, while the North Reef offers a gentler experience over a hard coral garden.
Koh Tachai
Famous for its pinnacle dive site known as Twin Peaks, Koh Tachai also offers more relaxed reef diving on the North Reef and South Reef. You can typically find turtles, barracuda, pipefish, and nudibranchs here. There is also a chance to see larger species like manta rays and whale sharks, especially from late January to April.
Richelieu Rock
This limestone pinnacle, named by Jacques Cousteau after Cardinal Richelieu, is covered in gorgeous purple dendronephthya soft corals and magnificent sea anemones. Barely breaking the surface at low tide, this horseshoe-shaped outcropping slopes steeply to a sandy bottom at 18 to 35 meters (60-120 feet). It offers great diversity for such a small and isolated spot, excellent multi-level diving, and sheltered areas to hide from currents. The marine life includes pharaoh cuttlefish, large octopuses, all five varieties of anemone fish of the Andaman Sea, various moray eels, ornate ghost pipefish, smashing mantis shrimp, harlequin shrimp, tiger tail seahorses, Spanish mackerel, frogfish, many schooling snapper, and occasional sightings of manta rays and whale sharks.
Surin Islands
Koh Surin's topside scenery, with evergreen forests, mangroves, and small beaches, surpasses even that of the picturesque Similan Islands. Underwater, the reefs of Surin boast some of the greatest hard coral diversity in Thailand. At sites like Torinla Pinnacle, Hin Kong, and Turtle Ledges, you are likely to see Napoleon wrasse, yellow-masked angelfish, bumphead parrotfish, tomato anemonefish, and barramundi, as well as many turtles that still come ashore to lay their eggs. Due to the remoteness, few liveaboard boats visit these islands, allowing you to enjoy the dive sites without sharing them with tourist hordes.