Most of the best things to do on Koh Samui happen on or in the water. The Gulf of Thailand is warm, mostly calm and dotted with islands, reefs and pinnacles, and the island's operators offer a wide range of trips from easy half days to demanding dive days. With so many choices, it helps to know what each activity involves, who it suits and how to fit it into a week. This guide compares the main options and explains how to choose.
Big-boat and speedboat island days
The classic choice is a full-day trip to Ang Thong National Marine Park, with 42 limestone islands, kayaking, snorkelling and a viewpoint hike. Big boats are cheaper and roomy, with lunch on board, while speedboats reach the stops sooner and spend more time in the water. Koh Tao and Koh Nang Yuan are the other headline trip, with a famous sandbar and some of the clearest snorkelling around. Both are long days and best taken separately, with a rest day in between.
Easy half days
If you want less time on a boat, Pig Island and Koh Tan make a pleasant half-day trip with beach stops, snorkelling and the chance to see the island's famous swimming pigs and, with luck, dolphins. These shorter trips suit families with younger children and visitors who are not sure they enjoy boats. The Koh Phangan junk boat cruise is a slower, more social day, with a sunset on the return.
Snorkelling
Snorkelling is included in most island tours, with equipment supplied. Reefs differ in quality, and visibility depends on weather, tide and season, with the calmer months generally the best. Wear a rash vest or T-shirt to protect against sun, use reef-safe sunscreen and never stand on or touch coral. Confident swimmers can go further from the boat, but weaker swimmers should use a flotation vest, which operators normally provide.
Scuba diving
Samui is a convenient base for diving. Introductory dives need no qualification, and the instructor looks after your equipment and depth, which makes them a good first step. Certified divers can book boat dives at Koh Tao, Koh Nang Yuan and Sail Rock, the open-water pinnacle known for big fish and a swim-through chimney. Allow for diving rules: complete the medical questionnaire, avoid alcohol the night before and do not fly soon after diving. Open-water courses run over several days if you want a certification.
Kayaking and paddleboarding
Kayaking is built into the Ang Thong day, where paddling between limestone walls and into a hidden lagoon is a highlight. Close to your hotel, you can often hire kayaks and paddleboards from the beach, and some operators run guided sunrise or sunset paddles in calm bays. These are gentle, low-cost activities that suit most fitness levels, and early morning is the calmest time.
Fishing
A small-group fishing trip gives a quiet, hands-on day on the water, with tackle supplied, help from the crew and a BBQ lunch of the catch. It suits families with older children and anyone who prefers a slower pace to a busy snorkelling boat. Serious anglers can look at private charters with bigger boats and deeper waters, though these are a much larger spend.
Sailing and sunset cruises
For a relaxed day without much effort, a catamaran or junk boat cruise offers sailing, swimming and a sunset. A private yacht charter is the splurge, with a chef, a crew and a route you choose. Dinner cruises combine a buffet with the view and suit groups who want a livelier evening.
Safety and etiquette
Always listen to the briefing, wear a life jacket where offered and tell the crew if you have a medical condition. Avoid touching marine life, do not feed fish and take your rubbish with you. Check the weather policy before you pay, because seas can be rough and boats cancelled, especially in the wetter late-year period, and choose free-cancellation options where possible. Bring a dry bag, a towel, a change of clothes and any seasickness medication.
Putting it together
A good water week might include one big island day, one easy half day, a sunset cruise and a rest day for each. Add a dive or a fishing trip if you want variety, and keep one spare day to catch up on anything that weather moves. Whichever you choose, start early, protect your skin and enjoy the water while it is calm.
