Trat and the Koh Chang Archipelago

The easiest window is November to April when seas are typically calmer, ferry crossings are smoother, and day boats can reach the national-park islands more reliably. Water is usually warm, around 27°C to 30°C, so comfort is rarely the limiting factor. The rougher, wetter period is generally May to October, when wind and rain can reduce visibility and cause same-day cancellations. If you want the best odds for the deep wreck plus reef variety, target December to March.

Trat and the Koh Chang archipelago see a pronounced rainy season roughly May to October. Rainfall can be heavy, and sea crossings to Koh Chang, Koh Mak, and Koh Kood can turn choppy, especially on exposed routes. Dive boats may switch to more sheltered sites or cancel if wind builds. If you travel in these months, book flexible tickets, avoid tight connections between islands, and plan extra buffer days. The upside is greener jungle scenery and stronger waterfalls, which can be a great topside tradeoff.

You have two main options. The fastest is to fly from Bangkok's Suvarnabhumi (BKK) to Trat (TDX), then take a short road transfer to the Laem Ngop pier area and hop on the ferry to Koh Chang (about 40 minutes in normal seas). The overland option is a direct road transfer from Bangkok to Trat or the pier area (roughly 315 km), which is useful if you have lots of dive gear. In monsoon months, build in extra time.

Island hopping is easiest in the calm season. Koh Chang connects to the mainland via frequent ferries, while Koh Mak and Koh Kood are commonly served by speedboat or catamaran from Laem Sok Pier. Some services stop at Koh Mak on the way to Koh Kood, which can save time and simplify logistics. In shoulder months and the May to October monsoon, inter-island routes may reduce frequency or pause, so plan your itinerary around confirmed boat days and keep a weather buffer.

For Koh Chang-based diving, the headline is the deep wreck at HTMS Chang Wreck. Pair it with structure and reef days at Hin Gra Dueng Pinnacle and relaxed coral time at Secret Reef. For shallow national-park style reefs, the Koh Rang area is a common day-boat target, including spots like Ko Rang North and Ko Rang Cave. Ask your operator to match sites to sea state, visibility, and your group's experience level.

Yes. Many sites in the region are shallow coral gardens and gentle slopes, which makes them well suited to Discover Scuba Diving, refreshers, and Open Water training. Koh Mak is often used as a quiet base for beginner programs, and Koh Kood's bays can feel relaxed when the surface is calm. Even if your group includes experienced divers, you can mix a deep wreck day on Koh Chang with easier reef days on park islands. Choose operators that brief buoyancy carefully and keep groups small.

Mu Ko Chang National Park charges an entrance fee for foreign visitors of THB 200 for adults and THB 100 for children. How you pay depends on the itinerary. Some trips pay at a park checkpoint, while others pay directly to rangers when you arrive at popular island stops. Either way, keep the receipt for the day because checks can happen at more than one location. If you are doing multiple park days, budget for multiple daily fees.

Water temperature is typically tropical year-round, often around 27°C to 30°C. Visibility varies more than temperature and can change with wind and recent rain. In the calmer November to April season, many divers report clearer days, while the May to October monsoon can bring lower visibility and more surge. A realistic planning range is about 5 m to 20 m, with better conditions after several calm days. Pack for sun and surface comfort as much as for warmth underwater.

Shore snorkeling depends heavily on sea state and access. Koh Kood has protected bays where reefs can be reachable from shore in calm conditions, including Soneva Reef and Hin Ao Yai. Go in the morning when wind is lighter, wear fins, and avoid snorkeling alone near boat lanes. If conditions are choppy, book a guided boat snorkel instead so the captain can move to a sheltered stop. On Koh Chang and Koh Mak, the best coral is often reached by boat day trips.

Plan one or two shared boat days that work for everyone, then let the group split. A typical pattern is: divers do a morning two-tank trip while non-divers join the same boat for snorkeling and beach stops, then everyone meets for lunch and a waterfall or sunset viewpoint in the afternoon. Koh Chang is the best logistics base for mixed groups because it has the widest range of tours and transport. Koh Kood is better for quiet beach recovery days. Build at least one no-plans day to absorb weather changes.

Bring a mix of cards and cash. ATMs are common in busier parts of Koh Chang and Trat town, but can be limited on smaller islands and remote bays. For internet, local SIMs and eSIMs are the simplest solution; AIS, True, and DTAC are widely used. Expect occasional slowdowns in remote areas and during storms. Download offline maps before moving islands and keep accommodation addresses saved for taxi rides. If you rely on mobile payments, keep a cash backup for piers and small restaurants.

For minor issues, island clinics and basic medical services can help, but treat serious dive injuries as an evacuation scenario. If you suspect decompression illness, stop diving, give oxygen if available, call Thailand emergency medical services (1669), and contact your dive operator immediately. Your operator can help coordinate transport to the mainland and onward referral. Do not self-diagnose or wait overnight. Dive accident insurance (for example DAN) helps with chamber referral and evacuation planning. Always carry your insurance details and emergency contacts on the boat.