Thailand has two coastlines, hundreds of islands, and water warm enough that a wetsuit never crosses your mind. You can float over a coral garden by nine and eat grilled squid on a beach by noon. But two separate monsoons mean the “best” coast depends entirely on when you go.
First Decision: Andaman Sea or Gulf of Thailand?
The two coasts have opposite rainy seasons:
The Andaman Side: Phuket, Krabi and Phi Phi
Phuket, Krabi, Ao Nang, Phi Phi and Koh Lanta are at their best from November to April — calm seas, clear water, every tour running. From May to October the southwest monsoon brings rough seas, and park islands like the Similans close completely. The limestone scenery here is more dramatic, and the snorkeling a notch better.
The Gulf Side: Samui, Phangan and Koh Tao
The Gulf islands get their heaviest rain roughly October to December, during the northeast monsoon. Their best months, February to September, make them the summer answer, when the Andaman side is choppy. Scenery is softer — granite boulders, not limestone cliffs — and Koh Tao has some of the country’s cheapest, easiest snorkeling, much of it straight off the beach.
The Main Bases
Phuket is the biggest hub: most tours, most departure times — and the biggest crowds. Krabi and Ao Nang are quieter; Ao Nang launches the 4 Islands and Hong Island trips. Koh Samui is the Gulf’s full-service base, running trips to Phangan, Tao and Ang Thong Marine Park. Koh Tao suits anyone who cares most about what’s underwater — you base yourself there and snorkel locally.
Famous Stops, Honestly Assessed
Phi Phi Islands and Maya Bay
Phi Phi is genuinely beautiful and genuinely busy. Maya Bay, on Phi Phi Leh, reopened after a long closure for ecosystem recovery, under strict rules: boats can’t enter the bay, you land at a rear pier and walk in, numbers are capped, and swimming is not allowed — though you can wade ankle-deep as reef sharks cruise the shallows. Take the earliest boat, or it feels like a queue with a view.
The 4 Islands Tour and Hong Island
From Ao Nang, the 4 Islands tour links Koh Poda, Chicken Island (named for a rock shaped like a chicken’s head), Tup Island — where a low-tide sandbar lets you walk between islands — and Phra Nang Cave Beach. Snorkeling is decent rather than spectacular, but it’s a hard day to beat for the price. Nearby Hong Island has a hidden lagoon, a viewpoint tower, and some of Krabi’s clearest water; many travelers prefer it.
James Bond Island
Khao Phing Kan is a fun photo stop — Koh Tapu’s needle rock looks impossible. But there’s no snorkeling, the stop is short, and boats funnel hundreds through a small viewing area. Book the Phang Nga Bay tour for its mangroves and sea caves; treat this as a bonus.
Similan Islands
If snorkeling is the whole point of the trip, come here. Reached from Khao Lak or Phuket, the Similans have Thailand’s clearest water and healthiest coral, with turtles a common sight. The park opens only from about mid-October to mid-May, numbers are limited, and tours sell out. Expect a 5 am pickup — serious snorkelers still rate it above everything else here.
Koh Tao
Shark Bay, Japanese Gardens off Koh Nang Yuan, Aow Leuk and Tanote Bay offer calm, shallow reefs reachable from shore or a cheap half-day boat. It’s also one of the world’s cheapest places to learn diving, and snorkeling trips cost half a Phuket tour. The blacktips at Shark Bay are harmless.
What a Group Tour Day Looks Like, and Costs
Most speedboat tours run the same rhythm: pickup around 7:30–8:30 am, a briefing at the pier, three to five stops mixing snorkeling (40–60 minutes in the water each time), a beach and a buffet lunch, back by 4–5 pm. Typical per-person prices, including transfers, mask, lunch and water:
- 4 Islands by longtail (Ao Nang): THB 600–900
- Phi Phi by speedboat: THB 1,300–2,200
- Hong Island by speedboat: THB 1,100–1,800
- Similan Islands day trip: THB 2,900–3,900
- Koh Tao snorkeling tour: THB 800–1,200
Park fees are often extra — roughly THB 200–400 per park for foreigners — so check before comparing quotes.
Private Longtail vs Speedboat
A private longtail (about THB 1,800–3,500 per boat) is slower and noisier, but you set the pace, beat the crowds and linger where the fish are — best value for groups around Krabi and Phi Phi. A speedboat covers far more ground — essential for the Similans — but shared tours run to a tight schedule and get bumpy in chop. Prone to seasickness? Sit at the back, and take a tablet before boarding, not after.
What to Bring
A rash guard and reef-safe sunscreen, a dry bag, a waterproof phone pouch, seasickness tablets, cash for park fees, and water shoes for rocky stops. Fins aren’t always included; ask when booking.
Reef Etiquette and Staying Safe
- Never touch, stand on or kick coral. It’s a living animal; one fin kick can break years of growth, and fire coral stings.
- Don’t feed fish or chase turtles and sharks. Let them come to you.
- Sea urchins hide in rocky shallows — look before putting a foot down. If spines go in, soak in hot water and see a clinic if pieces remain.
- Jellyfish appear mainly in wet months; a rash guard prevents most stings. Use vinegar, and get help fast for breathing trouble — box jellyfish, though rare, do occur.
- Currents run along headlands and between islands. Stay near your boat, snorkel with a buddy, and wear the life jacket.
Frequently Asked Questions
Which coast should I choose for my travel dates?
December to March: the Andaman (Phuket, Krabi, Similan) for the calmest seas and best visibility. May to September: the Gulf (Koh Tao, Samui), when the Andaman is rough.
I can’t swim well. Can I still snorkel?
Yes. Tours provide life jackets, guides choose shallow, calm spots, and many beginners simply float holding a ring. Tell the crew before the first stop; Japanese Gardens at Koh Tao is an ideal first reef.
Is Maya Bay worth it if I can’t swim there?
For most people, yes — the cliff-ringed bay is the sight, with sharks in the shallows as a bonus. In midday crowds it’s less worth it: take the earliest departure, or pick Hong Island instead.