Thailand is only 15 degrees north of the equator, giving it the benefit of a warm, tropical climate all year round. This means the ocean is also warm (so no need for a wet suit) and teaming with exotic sea life. The visibility is generally good and a great variety of coral and an even greater variety of fish can be seen from the surface, making many of the sites ideal for both snorkelers and divers. The reefs boast a vast array of corals including large sea fans, soft corals and giant table coral formations. Other common marine life includes barracuda, bat fish, grouper, octopus, angel fish, butterfly fish, parrot fish, flying fish, anemone, clown fish, wrasse, trigger fish, moray eels, hawksbill turtles, blue spotted stingrays and various reef sharks (don't worry, they are harmless to humans). Experienced divers can also explore the dramatic underwater landscape of the deep, including: ship wrecks, steep granite walls, caves, tunnels, coral-covered pinnacles, and open ocean seamounts.

It is possible to snorkel and dive in Thailand throughout the year. However, the country is subject to monsoons, which bring with them heavy rains and strong winds, so it's a good idea to make a note of the seasons and so avoid the regions that are subject to the bad weather.

The waters of the Gulf of Thailand, which is on the East coast, are somewhat protected within a large natural bay. This protection gives the region a number of quality dive sites that are accessible nearly all year, however the weather can get a little rough during November and December. The best dive and snorkeling sites in the region can be found around the islands of Koh Samui, Koh Pha-Ngan and Koh Tao. Scuba divers may also want to investigate some of the ship wrecks found in the Gulf, such as the HTMS Khram and the Hardeep, which sunk off the coast of Pattaya.

From November through to April, head to the West coast of Thailand and the waters of the Andaman Sea. Here, you will discover Thailand's best and most diverse underwater attractions. There are some great snorkeling and diving sites located to the east of Phuket. The world famous Koh Phi Phi, Hin Deang and Hin Muang are nearby, where enormous whale sharks and manta rays are regularly seen. Further south there is the island of Koh Lipe, where the reef is not far from the shore and so you can snorkel and dive straight from the beach.

The dive sites to the north of Phuket are only accessible via 'live aboards' (where you live onboard and dive from a boat). These sites include: the Similan Islands, Richelieu Rock, Koh Surin, the Burma Banks and the Mergui Archipelago. These sites are a real must for serious divers as they offer some of the best diving in the world.