There are 3 main diving routes that you can dive from a daytrip boat, as follows:
1) Racha Noi / Racha Yai Island
With shallow depth, calm, mostly sandy bottom, and clear water with minimum 15 meters visibility, it makes them a perfect spot for all dive training .The bottom can stretch down from 5 to 50 m deep. There are also artificial reef made by cement and shipwreck sunk down purposely to create home for the fish. It takes about 1.5 hrs from Chalong pier to the dive site by diving boat. Fish that can be commonly seen here are butterfly fish, lionfish, snapper, garden eel , batfish, barracuda and so on..
2) King Cruiser Wreck / Shark Point / Koh Doc Mai
This is suitable for divers with more experiences. King Cruiser wreck was a car and passenger ferry that sank on 4th May 1997 from an accident when the ship hit a submerged rock while going from Phuket to Phi Phi island. The wreck is 85 m long and 25 m wide and lies in an upright position. The depth is around 33 m at the bottom and about 18m on top.
Shark Point is only 5-10 min. by boat from King Cruiser wreck. It offers a diversity of fish and coral; and are covered with striking purple and pink soft corals. The maximum depth of this site is around 20-22 m.
Koh Doc Mai is a limestone island stretches vertically down to 24-28m that makes it a wall dive. Fish that are commonly seen from these 3 dive sites are snapper, eels, lionfish, pufferfish, anemone fish, bamboo shark and so on.
3) Phi Phi Island
The dive sites that are popular for scuba diving is a small rocky island called Bida Nok, located to the south of Phi Phi island. The depth starts from 6 m down to bottom of 20-25 m. Although the visibility is not always good, it has vast variety of Marine life. Leopard sharkis and blacktip reef shark may sometimes be found along the reef line. Look into the blue you may also see school of barracuda, yellow snapper, colourful reef fish such as pufferfish, porcupine fish and lionfish. It takes about 2.5 hrs from Chalong pier to the dive sites.