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Harelquin Shrimp
Koh Tao: Ao Chalok Baan Kao
The Gulf of Thailand
The Gulf of Thailand coast, at 1,840km well over twice as long as the Andaman Sea coastline, follows a great parabola from the border with Malaysia on the south coast around to Cambodia and the southwest tip of Vietnam. The Gulf itself is a vast, shallow depression – generally less than 60m deep and reaching a maximum of 85m – which, while incredibly productive, does not have continually great visibility.
This is largely due to the turbid waters from river outlets being trapped in the Gulf by an underwater shelf that stretches across the mouth of the Gulf from Malaysia to Vietnam. True reefs do not occur further north than those found in the Ban Krut area in Prachuap Khiri Khan Province, just over 300km south of Bangkok.
There are 112 islands in the offshore waters of the Gulf, many with fringing reefs interspersed with rocks and soft seabed. Visibility around their shorelines tends to be better than the mainland, where inshore waters are affected not only by turbidity but by freshwater runoff and urban/industrial pollution. The offshore reefs have a lower diversity than the reefs of the Andaman Sea, but marine life is still reasonably prolific, with Indo-Pacific species predominating.
Western Gulf
Some of the best dive sites in the Gulf of Thailand are around Koh Tao, 80km from the mainland. Sheer wall dives around submerged pinnacles, tunnels and archways carpeted with iridescent soft corals, pelagics (including sharks), and easy snorkelling from the beaches over impressive coral gardens are just some of the highlights of Koh Tao.
Koh Phangan, 47km south of Koh Tao, is a Bohemian paradise. The fringing reefs around the island are of limited appeal, but two sites to the north – Sail Rock and Samran Pinnacles – are truly world-class, spectacular wall dives, acting as a magnet for numerous schools of pelagics.
Koh Samui, further south, has a well developed tourist infrastructure and some enjoyable dive sites on its fringing reefs. Visibility around Koh Samui is only slightly better than that around Koh Phangan, and most people use it as a convenient (and fun) base from which to dive sites to the north of Koh Phangan or around Koh Tao.
Further to the south, the clear waters around Koh Losin, located above the Malaysian border, are occasionally dived from liveaboard excursions and are a great place for encountering manta rays, whale sharks and large schools of trevally.
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