Off the western coast of Thailand lie 52 islands that make up the archipelago of Koh Lanta. The largest islands, Koh Lanta Yai (big) and Koh Lanta Noi (little) are a tropical haven where travelers and tourists come to relax and unwind. Mountains covered in lush rainforest form a dramatic backdrop to 17 miles (27 km) of coastline, dotted with white, sandy beaches and mangroves. But Koh Lanta’s idyllic landscape isn’t the only draw — what lies beneath the ocean attracts scuba divers from around the world. Crystal-clear, warm waters offer great visibility, vivid colors, varied dive sites, and abundant marine life. From new divers to those with thousands of dives, the best scuba diving in Koh Lanta offers something everyone.
Nineteen miles (30 km) to the south of Koh Lanta are th two sister islands that comprise Koh Rok. Located in the Mu Koh Lanta National Marine Park, Koh Rok has some of the most pristine coral you will see in Thailand. The reef on the western side of the island slopes down to a sandy bottom at 65 feet (20 m) where you can see blue-spotted Kuhl’s stingrays.
The reef consists of hard corals where nudibranchs, octopus, moray eels, and lots of small fish hang out. Blacktip reef sharks are often active in the area around dusk and dawn.
The eastern tip of Koh Lanta features soft corals with huge gorgonian sea fans, coral trees, and sponges. Feeding turtles are the highlight here and you may spot pelagic fish like mackerel and cobia. Koh Rok really offers everything a diver wants.
Five large rocks make up Koh Haa, 15.5 miles (25 km) west of Koh Lanta. There are 10 different dive sites around the islands, each offering different topography and features that snorkelers and divers of all levels will enjoy.
Koh Haa Lagoon
Perfect for beginners is the lagoon at the center of Koh Haa. Depths range from 10 feet (3 m) on the inside to 40 feet (12 m) on the outside of the lagoon. Excellent visibility offers divers the chance to spot countless species including banded sea snakes, yellow boxfish, lionfish, butterflyfish, squid, stingrays, trumpetfish, and octopus. The lagoon is also a favorite with macro photographers looking for elusive seahorses, nudibranchs, frogfish, ghost pipefish, shrimp, and seamoths.
Koh Haa Yai
The largest of the Koh Haa islands is a playground for advanced divers with numerous caves, caverns, and swim-throughs. The largest cavern is known as The Cathedral, where natural light filters through the water, illuminating huge, ancient stalactites that hang from the ceiling. It’s possible to surface inside The Cathedral so you can really take in this magical sight. Many of the swim-throughs and caves are easily accessible for experienced divers, however some are not, and only specially trained cave divers should attempt entry.
Around Koh Haa Yai you will find leafy ghost pipefish, harlequin shrimp, and spiny lobsters hiding in cracks and crevices. Whale sharks often visit the island in April, you may be lucky enough to see whales passing by on their yearly migration.
A firm favorite with divers in Koh Lanta is Hin Muang, which means purple rock. This fully submerged pinnacle boasts the tallest vertical wall in Thailand, descending to over 197 feet (60 m).
The pinnacle is densely covered in purple soft corals with large white, red, and orange sea fans. Hin Muang is all about the bigger fish, with leopard and gray reef sharks hanging out in the deep, accompanied by huge schools of barracuda, tuna, and jackfish. Keep an eye out for smaller critters hiding among the anemones in the shallows. Don’t forget to look out in the blue where manta rays frequently fly through the water.
Conditions at Hin Muang are unpredictable. Strong currents and deep depths make it suitable for experienced divers only. But if you can stomach the rough 2.5-hour boat ride, Hin Muang is a dive not to be missed.
An hour speedboat journey brings you to the small, uninhabited island of Koh Waen. The diving around the island has loads to offer with plenty of overhangs and caves to explore. Giant porcupinefish, moray eels, nurse sharks, and stingrays take shelter here. Schools of yellowtail snappers and barracuda surround huge boulders, covered in sponges, corals, and anemones.
Koh Waen is also home to one of the most unique dive sites in the region. In 2015, Thai authorities sank a train to create an artificial reef. Since then its 20 wagons have become home to thousands of reef fish.
Yellow fusiliers, pufferfish, porcupinefish, and nudibranchs hide in and around the wagons. It’s not unusual to find nurse sharks underneath the wreck and stingrays in the surrounding sands. Schools of yellowtail and chevron barracuda prowl the area, hunting for prey. With a maximum depth of 60 feet (18 m) this is one train wreck every level of diver can enjoy.
When is the best time to go scuba diving in Koh Lanta?
Water temperatures vary slightly between 82 and 87 F (28 to 31 degrees C) during the year, making Koh Lanta a year-round diving destination. October to April is high season with December and January being the busiest times of the year.
During the low season (May to October), westerly monsoon winds blow in from the Indian Ocean bringing rain and the occasional thunderstorm. However, even though the weather is unpredictable, you can also expect long periods of sunshine and calm seas. Dive shops will vary their schedules during this time as some sites will be inaccessible, especially Hin Muang.
If you want to avoid the crowds, consider visiting Koh Lanta between February and April. This is also the best time to spot manta rays and whale sharks. Whatever time you choose to visit Koh Lanta, you are sure to enjoy all the diving these islands have to offer.