Koh Similan is by far the most beautiful group of dive sites that we have in Thailand and one of the best areas for diving in the entire world. Many people comment that the most fantastic thing about the Similans is that we have two radically different types of environments all rolled together into one destination. Nowhere else in the world will a diver find such diverse topography in such a small area.
The Similan Islands, located about one hundred kilometers northwest of Phuket, are composed of nine granite islands covered in tropical jungle, washed by a clear blue tropical ocean and blessed with some of the world's finest beaches. Similan comes from Malay fisherman who named it "The Nine Islands" (Similan is "nine" in Yawi, a South Thailand Malay dialect, and Sembilan is "nine" in Malay). The islands are identified by a name–in Thai–and a number; for example, Koh Huyong (Island #1), located at the southern end of the chain or Koh Miang (Island #4) located in the middle. The islands have achieved national park status and thus are fully protected under Thai law. The National Park Authority maintains their presence on two of the islands: Koh Similan (Island #8) the largest, and Koh Miang (Island #4). Recently, the islands have come to the special attention of the Thai Royal Family which further protects them from possible abuse. Currently there is limited accommodation available on the island, but hopefully soon this will be stopped as the island doesn't have the resources to support land-based tourism. There are no resorts on any of the islands and hopefully it will stay this way.
By drawing an imaginary line from north to south, we divide the area into our two separate types of environments. The East Coast with its powdery beaches features hard coral gardens which slope dramatically from the surface down to approximately 30-40m, where sand takes over as the water depth increases. On this side, the most popular activity is drift diving along healthy coral gardens while watching the reef inhabitants go about their business. In several sites, large coral bommies rise from the bottom and are covered with soft corals, sea fans, and an enormous amount of critters and unusual fish. Here the diving is easy and navigation simple, allowing each buddy pair to explore at his or her own pace.
The West Coast, just a short boat ride away, can offer faster paced, more exhilarating diving as currents swirl around the huge granite boulders–some larger than the largest of houses. These smooth, rounded boulders make dramatic formations, holes, and overhangs ("swim-throughs") underwater where divers can enjoy ducking through the openings. The drama of just looking up through the clear water at these huge rocks is satisfaction enough for some divers, as there are very few places like this on earth. Growing on these boulders are some of the most colorful soft corals imaginable, in many places so thick that the rock is no longer visible. In the larger passages or channels between the boulders, the fans grow to a size sometimes three-meters across, and are often so tightly bunched together that it makes it impossible to swim through the passages. Most of the dive sites on the West Coast are best seen with a guide, since navigation can be tricky.
If you enjoy watching and photographing small fish, the Similan Islands are hard to beat for the sheer numbers and varieties of tropicals especially lionfish and anemone fish. The Similans are not well known for consistent big fish-action, but we do see large trevally, some Napoleon wrasse and turtles. And luckily, we do get an occasional whaleshark and manta ray, while large cow tail rays are fairly common. And, of course the most famous aquatic resident of Thailand–the leopard shark–makes his appearance on a regular basis. As the park becomes more and more protected from illegal fishing, the fish are growing along with that protection. Overall, in my opinion, the reef fish are 20-30% larger than they were 20 years ago when I started diving here.
We'll also see white tip and black tip sharks once in awhile, a few times over the years we've seen schools of pseudo orcas or false killer whales and we get a lot of dolphins between the Similan Islands, Koh Bon and Koh Tachai. The point is, like all diving areas around the world, there is too much fishing going on to see big fish on every dive. Enjoy the Similans for what they are famous for; wild, unspoiled beaches, magnificent coral growth, prolific fish life, crystalline blue water and sensational underwater rock formations.
Trip lengths vary from three to five days; often longer if the boat is including the Similans as just one stop on the itinerary. One-day trips are possible at certain times of the year but in general are not recommended as it is impossible to fully appreciate the beauty of the islands without spending a few days diving around them. Also, two-stroke outboard engines are extremely polluting, and most of the boats offering one-day trips still use this type of engine. If you're not sure, ask. Trip prices vary dramatically depending on where you go and how comfortable you want to be.
High season in the Similans is from October until May, but diving is possible all year-round if the park is open (currently, it is not during the summer months). The water tends to be clearest in the summer and in the fall, but then again, the visibility is almost always good in the Similans, averaging approximately 18-25 m and at times exceeding 40m! There are well over 30 charted dive sites in the Similan chain, and the following short descriptions of a few of our favorites should give you an idea of what to expect.
A typical East Coast dive, this is my favorite way to begin a trip. The light is beautiful early in the morning hence its name, and the coral is in great shape. Down deeper in the sand, there has been a large increase of garden eels over the past few years. In the shallows, leopard sharks are often seen resting in the sand. Recently we've spotted a napoleon wrasse, which is a rare fish in the Similans.
One of my favorite dives, probably because this is where I saw my first whale shark, this reef features a steep drop-off with striking diversity of hard corals from 35m of depth almost all the way to the surface. This dive probably has the largest variety of healthy hard corals in the Similans, probably exceeding 300 species. I enjoy poking around the coral heads looking for nudibranchs and the nervous fire fish (Nemateleotris magnifica), one of the most beautiful fish in the tropical sea. One of the ugliest residents of this reef are the big eye fish that slowly cruise the reef flats. These fish have an amazing ability to change from a deep red color to a contrasting vivid silver. It almost appears as if they are changing their color to fit their mood.
Probably the most famous dive in the group, the site is named after an unusually shaped rock that juts out of the water just southwest of Koh Similan. The three rocks that form Elephant Head also create a natural amphitheater that feels like you are diving in a huge aquarium. Yellow goat fish and snappers always hang around at the deepest level of the bowl, as well as several species of lion fish, coral trout, and the occasional hawks bill or ridleys turtle. The swim-throughs at deeper depths are dazzling.
A typical East Coast dive, this particular site has one of the most incredible underwater bommies in the Similans. Beginning at about 21m and continuing up to about 12m, the concentration of marine life is unequaled in the Similans. For a period last summer, we had the opportunity to photograph a cute pink frog fish repeatedly, as he stayed in the same spot on the same reef for over two months. These are rare fish in the Similans anyway, but he was especially fun as he was so regally positioned on top of his throne of coral.
John Williams has written, co-authored, or contributed to four diving guides on Thailand, the Mergui Archipelago, and the Andaman Islands. These are the award-winning Lonely Planet Diving & Snorkeling series, Periplus Editions Diving Southeast Asia, Asian Diver Scuba Guides and Singapore's Times Edition Diving Thailand. He has lived in Phuket and dived in Thailand's waters since 1987.