Thailand in one water map

Thailand's dive planning is easiest when you think in two coasts:

• Andaman Sea (west coast): Seasonal marine-park access, big-visibility days, and the classic island loops from Khao Lak + Similan Islands, Krabi, and Koh Lanta.
• Gulf of Thailand (east and south): More year-round diving and freediving, with training hubs like Koh Tao, resort comfort on Koh Samui, and quieter trips from Chumphon.

Andaman Sea: marine parks and "big trip" sites

The Andaman is where Thailand feels like a liveaboard country. In the open season, water is commonly around 26°C to 30°C with visibility often 15 m to 30 m on settled days.

Start with:

• Richelieu Rock for schooling fish and occasional big-animal days.
• Similan boulders like Elephant Head Rock.
• Current-swept pinnacles like Koh Tachai Pinnacle and ridges like Koh Bon North Ridge.

Gulf of Thailand: training, pinnacles, and easy logistics

The Gulf is Thailand's skills-and-repetition engine. Many days are warm and approachable (often 27°C to 30°C), with visibility commonly 10 m to 30 m depending on wind and recent rain.

Anchor points:

• Koh Tao for courses, relaxed reefs, and offshore action.
• Pinnacle days at Chumphon Pinnacle and Sail Rock.
• Lower-crowd marine-park island hopping from Chumphon and laid-back Gulf islands in Trat and the Koh Chang Archipelago.

How to choose a region

If you want the "Thailand highlight reel"

Pick the Andaman in the dry-season window and plan around marine-park openings:

• Best bases: Khao Lak + Similan Islands and Koh Lanta
• Add-on islands: Koh Phi Phi and far-south Koh Lipe

If you want maximum water time for the least friction

Pick the Gulf and build a training-forward itinerary:

• Base on Koh Tao (scuba and freedive), with a resort reset on Koh Samui or party and beach time on Koh Phangan.
• Use Chumphon as the quieter mainland gateway.

Marine parks, rules, and what changed recently

• Marine national parks are a big part of Thailand's diving story. Expect park fees on many Andaman and island days, and respect mooring-only zones where anchoring is restricted.
• Thailand introduced stricter nationwide snorkeling and diving rules in April 2025 to reduce coral damage. Expect briefings, supervision ratios, and strict no-touch behavior in reef zones, especially for training dives.
• Some parks are moving to e-ticketing. Plan to keep a paper ticket or digital confirmation available for inspection.

A few trip shapes that work

• 7 days Andaman: 2 to 3 days based from Khao Lak + Similan Islands plus 3 to 4 days around Koh Lanta for Hin Daeng and Hin Muang.
• 7 days Gulf: Base on Koh Tao and time a pinnacle day to Sail Rock.
• 10 to 14 days "two coasts": Use Bangkok as your flight hub, then pick one Andaman window and one Gulf window to hedge against monsoon conditions.