Thailand's Coastline & Islands
Thailand possesses one of the most spectacular coastlines in Southeast Asia — approximately 3,219 kilometres of shore spread across two distinct bodies of water. The Andaman Sea coast faces west, exposed to the Indian Ocean's force and fringed with dramatic limestone karst formations, pristine coral reefs, and dense mangrove forests. The Gulf of Thailand coast curves from the southeast around to the south, offering calmer waters, powder-white beaches, and sheltered islands.
Between these two coasts lie more than 1,400 islands, ranging from vast inhabited islands like Phuket (the largest, at 543 km²) to uninhabited rocky outcrops barely breaking the surface. Many are protected as marine national parks. Together, they represent one of the world's premier concentrations of tropical island environments.
Andaman Coast
The Andaman coast stretches from the Myanmar border at Ranong province southward through Phang Nga, Krabi, Trang, and Satun. This coast faces the open Indian Ocean and is characterised by:
- Karst Limestone Formations — Towering limestone pillars, sea stacks, and mushroom-shaped rocks rising from emerald waters. The most famous: Phang Nga Bay, where hundreds of karst islands create a seascape of extraordinary beauty. James Bond Island (Ko Khao Phing Kan) and the Hong Islands archipelago are highlights.
- Deep Water & Strong Currents — The Andaman Sea is deeper and more dynamic than the Gulf. This supports richer marine biodiversity and better diving visibility, but also creates stronger currents and wave action, particularly during the southwest monsoon (May–October).
- Coral Reefs — The Andaman coast hosts Thailand's finest coral ecosystems, particularly around the Similan Islands and Surin Islands (both marine national parks). These reefs support whale sharks, manta rays, and some of the highest marine biodiversity density in the Indian Ocean.
- Mangrove Forests — Dense mangrove belts protect the coast, particularly in Phang Nga and Krabi provinces. Mangroves serve as nurseries for fish, buffer against storm surges, and sequester carbon at rates exceeding most terrestrial forests.
Key Andaman Islands
| Island / Group | Province | Highlights |
|---|---|---|
| Phuket | Phuket | Thailand's largest island (543 km²). Connected by bridge. International resort destination. |
| Phi Phi Islands | Krabi | Ko Phi Phi Don (inhabited) and Ko Phi Phi Leh (Maya Bay, now under visitor management). Dramatic limestone bays. |
| Similan Islands | Phang Nga | Archipelago of 9 islands. World-class diving. Open November–May only. |
| Surin Islands | Phang Nga | Remote archipelago near Myanmar border. Moken sea nomad community. Exceptional snorkelling. |
| Ko Lanta | Krabi | Laid-back island with long beaches and relaxed atmosphere. Two islands joined by bridge. |
| Ko Lipe | Satun | Thailand's southernmost resort island, near the Malaysian border. Tarutao Marine National Park. |
| Ko Tarutao | Satun | Former political prison island, now a pristine national park. Wild, undeveloped, atmospheric. |
| Ko Yao Noi / Ko Yao Yai | Phang Nga | Twin islands in Phang Nga Bay. Muslim fishing communities, rubber plantations, low-key tourism. |
Gulf of Thailand Coast
The Gulf coast runs from the Cambodian border at Trat province, curving south through Chonburi (Pattaya), Rayong, Prachuap Khiri Khan (Hua Hin), Chumphon, and Surat Thani, before reaching the deep south at Songkhla and Narathiwat.
Gulf waters are generally calmer, warmer, and shallower than the Andaman Sea. Characteristics include:
- Calm Waters — The Gulf is semi-enclosed, creating gentler wave action and more predictable conditions. This makes Gulf beaches particularly suitable for swimming and kayaking.
- Different Monsoon Pattern — The Gulf coast's rainy season peaks in November–December (northeast monsoon), not May–October like the Andaman coast. This means the Gulf is at its best from February to September, making it possible to find good beach weather somewhere in Thailand year-round.
- Sand Beaches — Long stretches of white and golden sand, particularly on the islands and the Prachuap Khiri Khan coastline.
Key Gulf Islands
| Island | Province | Highlights |
|---|---|---|
| Ko Samui | Surat Thani | Thailand's second-largest island after Phuket. International airport. Coconut palms, resorts, Big Buddha. |
| Ko Phangan | Surat Thani | Full Moon Party on Haad Rin. Northern beaches are tranquil. Yoga and wellness retreats. |
| Ko Tao | Surat Thani | World's cheapest and most popular place to learn scuba diving. Laid-back, backpacker-friendly. |
| Ko Chang | Trat | Thailand's second-largest island by area. Mountainous interior with waterfalls. Eastern Thailand's beach destination. |
| Ko Mak | Trat | Small, flat, car-free island. Peaceful, family-friendly. Rubber and coconut plantations. |
| Ko Kut (Ko Kood) | Trat | Thailand's fourth-largest island. Relatively undeveloped. Pristine beaches, waterfalls, clear water. |
| Ko Samet | Rayong | Weekend escape from Bangkok (4 hours). Small, pretty beaches. National park. |
The Peninsula
Southern Thailand narrows dramatically into the Malay Peninsula, a land bridge barely 44 kilometres wide at the Kra Isthmus (in Ranong/Chumphon provinces). This geographic pinch point means you can drive from the Andaman coast to the Gulf coast in under an hour. An idea to build a canal across this isthmus — the Thai Canal or Kra Canal — has been discussed for centuries and would revolutionise Asian shipping by bypassing the Strait of Malacca, though the project remains politically and environmentally contentious.
South of the isthmus, the peninsula widens again before narrowing at the Malaysian border. The west coast (Andaman side) remains predominantly Buddhist Thai, while the deep south (Gulf side, Pattani/Yala/Narathiwat) has a Malay Muslim majority population.
Coastal Threats
Thailand's coasts face significant environmental challenges:
- 2004 Indian Ocean Tsunami — The devastating Boxing Day tsunami killed over 5,000 people in Thailand, with the Andaman coast (particularly Khao Lak and Phi Phi) suffering catastrophic damage. Thailand has since invested heavily in early warning systems.
- Coral Bleaching — Rising sea temperatures have caused major bleaching events, particularly in 2010, 2016, and 2024. Some reefs have recovered; others have not.
- Coastal Erosion — Construction, sand mining, and mangrove removal accelerate erosion in many areas.
- Overtourism — Maya Bay was closed for years to allow recovery. Visitor caps now limit access to sensitive sites.
- Plastic Pollution — Marine plastic remains a major challenge, though beach cleanup initiatives and plastic bag bans have improved conditions.