Diving in Similan Islands

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Conditions

Water temp

27–30 °C

Visibility

15–40 m

Depth

2–40 m

Current

Moderate

Best season

Jan–Apr (NE monsoon: calm seas, peak visibility 25–40m, best for whale sharks and manta rays)

Month	Summary
Jan	Peak season with 25–40m visibility and calm seas. Manta rays frequent Koh Bon Ridge and Koh Tachai Pinnacle. Leopard sharks rest on sandy channels throughout the inner islands. Whale sharks possible at Richelieu Rock.
Feb	Peak whale shark month at Richelieu Rock with sightings reported weekly. Visibility 25–40m. Manta ray cleaning stations active at Koh Bon and Koh Tachai. Best month for combining big-animal encounters with excellent photography conditions.
Mar	Whale shark peak continues at Richelieu Rock. Visibility 20–35m. Manta rays still present at northern pinnacles. Sea temperatures warm to 28–29°C. Last month of guaranteed calm before transition.
Apr	Tail end of whale shark season — still good encounters at Richelieu Rock. Visibility 20–30m. Manta rays remain at Koh Bon. Warmer water 28–30°C. Turtle nesting activity near season end. Quieter as low-season approaches.
May	First half of May: last chance before park closure. Visibility 15–25m with transition conditions. Manta rays and reef sharks still active. Warmer water 29–30°C. Fewer boats, more solitude. Park closes mid-May for monsoon.
Jun	Park CLOSED — southwest monsoon. No diving or tourism permitted. Reef recovery period. Best month for planning next season's trip and booking early-bird liveaboard deals for October reopening.
Jul	Park CLOSED — southwest monsoon continues. Heavy rainfall and rough seas. Coral spawning events occur naturally during this period. Reef ecosystems regenerate without diver pressure.
Aug	Park CLOSED — peak monsoon month. Strongest winds and heaviest rainfall. Nutrient-rich upwelling builds plankton blooms that will feed the coming season's manta ray and whale shark aggregations.
Sep	Park CLOSED — monsoon begins to ease toward month end. Operators prepare vessels and equipment for October reopening. Last chance for early-bird booking discounts before season starts.
Oct	Park REOPENS mid-October. Visibility 15–25m — improving through the month. Manta rays return to Koh Bon cleaning stations. Reef fish abundant after 5-month rest. Fewer divers, excellent value. Some sites still limited by residual swell.
Nov	Transition month with improving conditions. Visibility 20–30m. NE monsoon establishes, calming seas. Manta rays active at Koh Bon and Koh Tachai. Whale sharks begin appearing at Richelieu Rock. Great month for value before peak-season crowds.
Dec	Dry season in full swing with 25–35m visibility. Calm seas, sunny skies. Manta rays resident at northern pinnacles. Leopard sharks return to sandy channels. Eagle rays and reef sharks throughout the islands. Holiday season brings more liveaboards — book early.

Dive Sites (42)

Beacon Point (Koh Payu East)

5–25m · Beginner

Leopard shark sightings · Coral slope · Sandy channels

Christmas Point

5–30m · Beginner

Reef sharks

Coral-encrusted boulders · Eastern aspect

Coral Reef (Koh Pa Yang East)

3–18m · Beginner

Coral garden

Staghorn coral · Table coral

Deep Six

8–35m · Advanced

Swim-throughs · Macro life

Boulder field

Donald Duck Bay (Ao Luk)

1–8m · Beginner

Snorkeling

Granite boulder beach · Turtle encounters

Elephant Head Rock (Hin Pusa)

3–35m · Advanced

Swim-throughs

Granite boulder labyrinth · Tunnels and arches

Fantasy Reef (Koh Pa Yan West)

10–35m · Advanced

Granite boulders · Pelagic action · Deep wall

Garden of Eden

3–25m · Beginner

Mixed boulder and coral · Turtle encounters · Milder currents

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Regional species catalogue (82)

Species recorded in this destination's wider regional catalogue. A species being listed here does not mean it is seen at this destination — check the note on each card.

Great Hammerhead

General species description, not specific to this destination

The Great Hammerhead is the largest of all hammerhead species, instantly recognizable by its massive, flattened head extension called a cephalofoil. This prehistoric-looking predator can reach lengths of up to 20 feet, with a distinctive tall, sickle-shaped dorsal fin. Their unique head shape houses electroreceptors that help them hunt stingrays buried in sand. Great Hammerheads are solitary hunters, often seen cruising along reef walls and sandy bottoms. Despite their intimidating size, they're generally shy around divers and will often move away when approached. Their powerful swimming style and graceful movements make encounters truly memorable for fortunate divers.

Spotted Eagle Ray

Destination note

Frequently observed in pairs or small groups at western reef slopes. More common in peak season months. Park closed Jun-Oct.

Green Sea Turtle

Destination note

Commonly sighted across all sites, especially seagrass beds on eastern side. Nesting season Apr-May. Park closed Jun-Oct.

Hawksbill Turtle

Destination note

Common across all reef sites. Frequently observed at coral-rich areas like Richelieu Rock and eastern slopes. Park closed Jun-Oct.

Atlantic Bottlenose Dolphin

Destination note

Sighted during surface intervals and boat transits between sites. More frequent during calm conditions Jan-Apr. Park closed Jun-Oct.

Bull Shark

Destination note

Rare but regularly reported at Koh Tachai and Richelieu Rock deeper pinnacles. Park closed Jun-Oct.

Loggerhead Turtle

Destination note

Rare visitor to Similan waters. Most likely encountered at Richelieu Rock during peak season. Park closed Jun-Oct.

Photo: Centropyge multifasciata.jpg — desertnaturalist · CC BY 4.0 · Full source frame fitted to a square canvas; resized and encoded as WebP for main (1280×1280) and thumbnail (400×400).

Multibarred Angelfish

General species description, not specific to this destination

A small angelfish with a compressed body, alternating dark and pale vertical bars, and yellow accents on the face and fins. It is shy and often stays close to reef crevices, slopes, and overhangs. The barred pattern and small size distinguish it from larger, more boldly colored angelfishes.

Common Lionfish

General species description, not specific to this destination

The stunning Common Lionfish is immediately recognizable by its dramatic fan-like pectoral fins and bold red, white, and brown stripes. These graceful predators glide slowly through the water with their venomous spines spread wide like a feathered headdress. Despite their beauty, lionfish are aggressive hunters that use their large mouths to vacuum up small fish and crustaceans. Originally from the Indo-Pacific, they've become established invaders in Caribbean waters. Divers often spot them hovering near coral formations or rocky overhangs during the day, moving with deliberate, almost theatrical movements. Their confidence underwater is striking – they rarely flee from approaching divers, making them excellent photography subjects when observed from a respectful distance.