The biggest of the Haa islands is Koh Haa Yai. It is characterized by a steep cliff perpendicular to sea level that stretches all the way from above the water to depths of up to 30 m. Koh Haa Yai is surrounded by reefs, and the most famous dive spot is the rock wall at the south side of the island, which ends in a sandy bottom at 25-30 m. It is covered with a variety of soft corals, sea fans and hard corals.
There are two underwater caves on the southeast side The entrance of the first cave is at a depth of 12 m.
Note: Since this cave gets narrower as you go deeper, cave penetration is not recommended unless divers have obtained cave diving certification or are in training with qualified instructor.

The second cave is actually a shallow cavern and can be found to the east of the first cave. The entrance is split into two by a vertical rock plate, but the rest of the cave is spacious and well illuminated. The hall height of the cave is 2-3 m above sea level, so swimming to the surface from inside the cave is possible. This cave is also known as “The Cathedral” because of the blue light reflected from the surface. The Cathedral is the highlight of this divesite. The exterior of the cave is covered with soft corals, sea whips and rock outcrops, ending in a sandy bottom at depths of 28-30 m. Leopard sharks and Kuhl’s sting- rays are often found around the sandy bottom. Juvenile lobsters and a variety of nudibranchs can be spotted around crevices at the cliff, especially at the entry of the cave.
If you look closely, you may also find ghost pipefish camouflaged among sea fans or soft corals! Schools of squid and yellowtail barracuda are frequently seen near the surface close to the cave’s entry. Reflection from schools of copper sweepers can be seen when you shine a light into the cave. Hawksbill turtles have also been spotted in the area.

Note: In the event of strong surges or rough waters, divers should avoid going inside the cave due to the risk of being pushed against the cave wall and suffering injury from sharp rock outcrops or stings from residents on the walls.

Note: Koh Haa Yai is often dived on a Dive Cruise to Koh Lanta or https://alohadiving.com/product/hin-deang-hin-muang-itinerary/.