The Similan Islands are by far the most spectacular group of dive sites that Thailand has to offer and are on par with some of the best diving destinations worldwide.
The island of Koh Tachai lies about 20 nautical miles South of Richelieu Rock and can be another great spot for Manta Rays. The dive site is a submerged sea mount with depths from 14-35m, and currents can be quite strong.
The top of the reef is a beautiful mixture of hard corals, while deeper regions consist of scattered boulders and sea fans. Leopard sharks are commonly found resting on the bottom, while schools of barracuda and batfish cruise around the reef.
Koh Bon is only a short cruise North of the Similan Islands and is without doubt the best site for Manta Rays. The dive site follows a ridge, covered in pastel shaded soft corals, which drops to depths of 35-40m.
Mantas are often spotted over the ridge or in the deep water to the South. Leopard sharks are also common in the deeper water and this is a good location to find the elusive purple fire goby.
Some 50 nautical miles North of the Similan Islands lies one of the best known dive sites in Asia. Just breaking the surface at low tide, Richelieu Rock is probably your best chance to have the whale shark experience.
Some years ago, this site was regarded as a "whale shark magnet", and while this is somewhat of an exaggeration, they still visit regularly. Other large pelagics such as eagle and manta rays are common visitors.
The site is huge and most live-aboards will schedule more than one dive here. The sheer variety of life is amazing. Huge schools of trevallies and barracudas cruise the currents, and many tiny critters such as frogfish, ghost pipefish and seahorses are hiding in cracks and crevices.
Richelieu Rock is one of the finest sites in Thailand.