Rated as one of the world’s best spots for both above-water and underwater beauty, the eleven islands at the heart of the Mu Ko Similan National Park are among the most exciting diving destinations in Thailand. Massive granite boulders set magnificently against turquoise waters give the islands their distinctive character, but it’s the 30m visibility that draws the divers. The 5000-year-old reefs are said to be the oldest in Thailand, so there’s an enormous diversity of species, and the underwater scenery is nothing short of overwhelming: the reefs teem with coral fish, and you’ll also see turtles, manta rays, moray eels, jacks, reef sharks, sea snakes, red grouper and quite possibly white-tip sharks, barracuda, giant lobster and enormous tuna.
The islands lie 64km off the mainland and include the eponymous Ko Similan chain of nine islands as well as two more northerly islands, Ko Bon and Ko Tachai, which are both favoured haunts of manta rays and whale sharks and are halfway between the Similan chain and the islands of Ko Surin. The Similans are numbered north–south from nine to one and are often referred to by number: Ko Ba Ngu (9), Ko Similan (8), Ko Payoo (7), Ko Hin Posar (aka Ko Hok; 6), Ko Ha (5), Ko Miang (4), Ko Pahyan (3), Ko Pahyang (2) and Ko Hu Yong (1). The national park headquarters and accommodation is on Ko Miang and there’s also a campsite and restaurant on Ko Similan. Ko Similan is the largest island in the chain, blessed with a beautiful, fine white-sand bay and impressive boulders and traversed by two nature trails; Ko Miang has two pretty beaches, twenty minutes’ walk apart, and three nature trails; Ko Hu Yong has an exceptionally long white-sand bay but access is restricted by the Thai navy as turtles lay their eggs there from November to February.
Such beauty has not gone unnoticed and the islands are extremely popular with day-trippers from Phuket and Khao Lak, as well as with divers and snorkellers on longer live-aboard trips. This has caused the inevitable congestion and environmental problems and the Similan reefs have been damaged in places by anchors and by the local practice of using dynamite in fishing. National parks authorities have responded by banning fishermen and enforcing strict regulations for tourist boats, including closing the islands during the monsoon season, from May to October.