Known as the "Jewel of diving Thailand’s Marine National Parks," the Similans include nine rocky islands boasting dozens of excellent sites.
Sparkling water and sugary beaches surround the islands' lush green interiors, creating remarkable topside scenery. Below the surface, eastern reefs like Morning Glory are sloping coral gardens, while west-side sites like Christmas Point and Elephants Head feature huge granite boulders, caverns and passageways. Both sides boast abundant soft corals, barrel sponges and fans, plus critters like mantis shrimp and assorted nudibranchs. Fish diversity is exceptional, including exotics like frogfish and ribbon eels, as well as endemics like Andaman sweetlips.
North of the Similans' main group lies Koh Bon, a small island where a jagged ridge plunges to meet a sandy plateau, attracting schooling snappers and bluefin trevally. Nearby, a deep pinnacle covered with small, yellow soft corals is a good place to encounter friendly zebra sharks. At Koh Tachai, twin rocky pinnaclesoften hum with activity, as queenfish and barracuda patrol midwater, while batfish line up to be cleaned on the reef. Mantas are sighted regularly at Koh Bon and occasionally at Tachai.
An isolated pinnacle that barely reaches the surface, Richelieu Rock is a perfect multilevel dive, and arguably best Thailand's diving site. An incredible variety of creatures live here, including dense colonies of anemones and soft corals. White-eyed morays scurry about investigating crevices, followed closely by gangs of snapper, grouper and lionfish. Almost anything can show up at Richelieu, including rarities like harlequin shrimp, seahorses, ghost pipefish and even whale sharks.
While most of the best Thailand diving areas are northwest of Phuket, Hin Daeng (Red Rock) and nearby Hin Muang (Purple Rock) lie well to the south. Only a stone's throw from each other, both sites are limestone pinnacles that tumble dramatically to 160 feet, creating Thailand's diving deepest wall. Residents include giant morays, cuttlefish, zebra sharks, red- bar anthias and a wide assortment of reef fish. Hin Muang also features thriving soft corals and vast fields of anemones. Another southern site is a towering limestone island called Koh Ha Yai, where it's possible to surface into an air chamber inside a huge double cavern. When conditions are right, you can float on the surface and watch as clouds form among the stalactites, then disappear every few seconds when swells cause air pressure to fluctuate inside the chamber (diving asia).
Thailand's reefs experienced unusually warm water temperatures in 2010, causing significant coral bleaching. Certain species were unaffected, but some hard corals in shallow areas have died. Obviously this development is troubling, but divers should note that the soft corals, sponges, fans and fish life remain as healthy as ever, providing plenty of spectacular underwater scenery. To reduce stress on affected areas, Thai authorities have temporarily closed several reefs to divers.