To the South of Phuket lie the twin islands of Ko Racha Yai (big) and Ko Racha Noi (small) which offer significantly better diving than do Phuket's Western beaches. Almost all diving operators offer one day trips to both of the islands (although not on the same day) and some offer a two day liveaboard trip every week.
Racha Yai's best diving is off its East Coast which makes it especially attractive during Phuket's off-season in the summer. Although visibility varies, it can be as good as 25 meters or more. A typical dive is a gentle drift along a sloping rocky face that is sprinkled with hard coral forests of many varieties. Especially prominent are stag horn corals of blue and tan. Many times there are large schools of false barracudas hovering over the reef, while on the reef itself you'll see octopus and cuttlefish in addition to the more common tropical species. Divers of all levels of experience and snorkellers can visit Racha Yai with no usual hazards as the diving is easy and gentle. Water depths range from 3 to 30 meters.
Racha Noi is popular for the more experienced diver, as depths are generally greater and the currents frequently stronger than at its sister island to the North. The Northern tip feature a large pinnacle where spotting larger marine life is distinctly possible, while the Southern point is a nice drift dive with the added bonus of having a beautiful little beach to visit during your surface interval. We also have a wooden ship wreck at about 27 meters on the Southwest Coast of the island which although it does not compare to some of the larger wreck dives in Pattaya, is an enjoyable deep dive. Not much grows on the wreck yet, but it attracts large amounts of reef fish. The diving here is definitely more challenging than Racha Yai, but the rewards can be much greater.
Accommodation is available on Racha Yai in both of the pristine little bays on the Northern side of the island. Muslim farmers and a few fishermen have lived on Racha Yai for years now, harvesting coconuts and fishing the waters surrounding the islands. (Until a few years ago, Marijuana was a popular crop here, but that has been stopped by local authorities.) Although there are no established dive shops on the island, occasionally someone tries to make a go of it. It is often possible to be picked up on the island by one of Phuket's dive boats. For current information, check with one of the dive centers in Phuket.
This text is taken from the original award-winning Lonely Planet's Diving and Snorkeling Thailand, by Mark Strickland and John B Williams. This original version is no longer in print but still available from Amazon and other sources. Visit Mark's website for beautiful underwater photography.