The best and most popular snorkelling is at the islands of Ko Rok Nai and Ko Rok Nok, 47km south of Ko Lanta; these forested twins are graced with stunning white-sand beaches and accessible waterfalls and separated by a narrow channel full of fabulous shallow reefs. Also hugely popular is the “four island” snorkelling trip that takes in the much nearer islands off Trang – the enclosed emerald lagoon on Ko Mook, plus nearby Ko Hai (Ko Ngai), Ko Ma and Ko Kradan – but these sites can get very crowded. Another option is the day-trip to Phi Phi Don, Phi Phi Leh and Bamboo Island. The trips cost around B1500 in a speedboat or B900 in a big boat, including lunch, snorkelling equipment and national park entry fee. For a smaller, more personal experience, contact Sun Island Tours or Freedom Adventures.
The reefs around Ko Lanta are quieter and in some cases more pristine than those round Phi Phi and Phuket, and excellent for seeing whale sharks. The diving season runs from November to April, though a few dive shops continue to run successful trips from May to August. All dive boats depart from Ban Sala Dan, and nearly all dive courses are taught either in Sala Dan or on Hat Khlong Dao, though there are dive shops on every beach.
Some of Lanta’s best dive sites are located between Ko Lanta and Ko Phi Phi, including the soft coral at Ko Bidah, where you get lots of leopard sharks, barracuda and tuna. West and south of Lanta, the Ko Ha island group offers four different dives on each of its five islands, including steep drop-offs and an “underwater cathedral” and other caves; visibility is often very good. Much further south, about 56km from Ko Lanta, are Hin Daeng and Hin Muang.
The nearest recompression chambers are located on Phuket; check to see that your dive operator is insured to use one of them (see Diving and snorkelling).
There are several rewarding kayaking destinations, rich in mangroves and caves, around Ko Lanta Yai’s east coast and around Ko Lanta Noi and its eastern islands, including Ko Talabeng and Ko Bubu; a few companies also offer kayak-snorkel trips to the four islands described above.