You can rent snorkelling equipment (B100/day at Coco Cottage, for example) and kayaks (B50/hr at Koh Ngai Villa, for example) at most of the resorts. All the resorts offer boat trips (B1500/boat, or B300/person in a group of six, at Ko Hai Seafood, for example) that take in the Emerald Cave on Ko Mook and some snorkelling off Ko Hai. (Ko Cheuak, just to the southeast of Ko Hai, is currently off-limits to visitors to protect the coral, which was badly bleached during a sudden rise in sea temperatures in 2010 – avoid any place that offers trips there.) Ko Hai Seafood can also put together overnight snorkelling and camping trips to Ko Rok for B2300 per person.
Towards the southern end of the beach, Fantasy Resort has a well-organized dive shop, the German-run Rainbow Divers.