The best dive season to dive Koh Chang starts from October / November to April
The visibility is generally between 5-15 metres (16-49 feet) and the best sites are situated on the west and south of Koh Chang which boasts an abundance of brightly coloured, healthy and unspoiled corals and a great diversity of fish. There are more than 10 dive sites in Koh chang.
Some of the dive sites on Koh Chang are:
Hin Rap, located off the small island of Klo Klum. There are occasional currents and it's composed of rocky reef
covered in barrel sponges, soft sponges and gorgonians.Many small reef fish such as fusiliers, gobys and anthias are found here.
Hin Luk Bat is very close to Koh Chang is characterised by it's abundance of healthy soft corals. Several shelves around this pinnacle provide homes for smaller reef organisms and crustaceans.
The currents are weak and visibility goes to about 15 metres (49 feet). You may encounter crown of thorns
Koh Wai reef has a lot of hard corals such as plate and brain with softer corals deeper down. The depths are between 5-20 metres (16-65 feet) and rays are often encountered here.
Koh Rang Pinnacles is a series of pinnacles with a coral shelf at about 15 metres (49 feet). Living here is a variety of marine life which includes angelfish, parrotfish, tuna and barracuda.
Koh Kra is a small rocky islet with a shallow fringing reef teeming with life. This site is exceptionally shallow not exceeding 10 metres (33 feet). Shallow coral gardens slope gradually giving way to a sandy bottom usually harboring rays.
The Thonburi is a Thai warship sunk by the French navy in the 1940's. This wreck lies in shallow waters near the Salak Petch Bay, south of Koh Chang. The visibility is poor here and there may be strong currents.