Trip report | Thailand | South & North Andaman Expedition, 29th March – 5th April 2026

Andaman Sea Expedition: From Koh Phi Phi to Richelieu Rock

This expedition through the Andaman Sea unfolded as a gradual exploration of both landscapes and marine life, shaped by shifting currents, encounters, and the quiet surprises hidden along the reefs. While we don’t have photos for every sighting, we had some really special encounters!!! The highlight was probably a snaggletooth shark and a Bowmouth guitarfish, two very rare encounters among the many sharks and rays seen this week!!!

From the dramatic limestone formations of the South Andaman to the exposed pinnacles of the North, each dive revealed a new layer of biodiversity. From the sheltered bays of Koh Phi Phi and Koh Lanta to the dynamic sites of the Similan and Surin National Parks, the week developed into a seamless blend of colourful reefs, schooling fish, and intricate macro life.

Day 1 – From Phuket to Koh Phi Phi National Park

We departed this adventure from Phuket with our guests from France, the UK and the USA, setting course towards the iconic Phi Phi Islands. Known for their towering limestone cliffs and emerald waters, the islands also shelter vibrant reefs teeming with life.

Anchored beneath the cliffs for the night, the atmosphere was calm and promising — a quiet beginning before the rhythm of diving took over.

Several Moorish Idols swimming in front of a massive swirling silver bait ball in the deep blue Andaman Sea. — Contrast in the blue: Elegant Moorish Idols drift past a colossal bait ball, showcasing the immense scale of marine life in the Similan Islands.

A dramatic sunset over the ocean with orange and pink crepuscular rays fanning out across a darkening sky near rocky islets. — Nature’s light show: Stunning crepuscular rays paint the sky over the North Andaman Sea, marking the end of another spectacular day of diving.

Day 2 – Koh Phi Phi & Koh Lanta National Park

Our check dive at Bida Nok immediately set the tone. Hypselodoris purpureomaculosa added colour to the reef alongside ghostpipefish and flounders resting on the sand. A hawksbill turtle cruised by while a group of ten blacktip reef sharks patrolled the shallows. A tigertail seahorse clung delicately to the reef, while purple urchin shrimps moved among spines.

Around them, schools of five-lined snappers, yellowback fusiliers and Moorish idols filled the water column, joined by butterflyfish, surgeonfish and parrotfish grazing the reef.

Macro life was already hinting at what was to come — a richness that would only intensify as the expedition progressed.

A Blacktip Reef Shark swimming over a rocky reef accompanied by a small school of yellow snappers in the Andaman Sea. — Grace in the shallows: A Blacktip Reef Shark glides effortlessly past a school of snappers, captured in the pristine waters of the Similan Islands. | Renaud Liberge

A close-up view of a Hawksbill Turtle swimming gracefully over a colourful coral reef in Thailand. — A gentle encounter: A beautiful Hawksbill Turtle navigates the vibrant coral gardens of the North Andaman Sea. | Frederique Bechet

Moving on to Koh Lanta National Park, we started with a macro treasure hunt at Koh Haa Cathedral. Noumea norba, Bornella, Phyllidiopsis striata, Halgerda bacalusia (candy halgerda) and Halgerda willeyi decorated the walls, while an Anker whip coral shrimp carrying eggs hovered delicately. Coral groupers, copperband butterflyfish, Indian sailfin tang and cleaner wrasse completed the scene.

A bright orange Vermilion Grouper resting among white and pink soft corals with a school of small reef fish in the blue Andaman Sea. — A splash of colour: A Vermilion Grouper finds shelter in a garden of soft corals, a testament to the thriving marine life of the Similan Islands.

A macro close-up of a mosaic-patterned Bornella anguilla nudibranch with orange-tipped rhinophores crawling on a bright yellow sponge. — Mosaic of the reef: The incredible detail and vivid colours of a Bornella anguilla nudibranch captured against a luminous yellow background.

At Hin Daeng & Hin Muang, the pace picked up with schools of rainbow runners, giant trevallies and bluefin trevallies hunting in the blue. Batfish hovered mid-water, a hawksbill turtle passed by, and ghostpipefish blended into the reef. Jellyfish drifted through the current while juvenile emperor angelfish, bentstick pipefish, juvenile brown coral blenny, peacock mantis shrimp and longnose hawkfish kept divers scanning every corner.

Schools of fusiliers, snappers and surgeonfish added constant movement.

A group of Longfin Batfish swimming through cathedral-like sunbeams in the clear blue waters of the Andaman Sea. — Underwater cathedral: Longfin Batfish glide through spectacular light rays, a serene moment captured during our deep blue exploration.

A school of predatory trevally diving into a massive dense bait ball of smaller fish in the open ocean. — The hunt is on: Predatory Trevally strike with lightning speed, scattering a massive bait ball in a display of raw reef energy.

The night dive at Hin Daeng revealed Noumea sp., Hypselodoris sp., swollen bubble snails, barred-fin moray and minor moray, along with blacktail Zanzibar urchin shrimp, skeleton shrimp, tapestry shrimp and spotted reef crabs. Around them, sleeping parrotfish, hunting lionfish and active shrimps completed the nocturnal reef.

A tranquil sunset over the Andaman Sea with dark rocky formations in the foreground, marking the start of Day 3 in Koh Tarutao National Park. — Golden hour at Koh Tarutao: The sun sets over the calm horizon as our expedition moves into the southern reaches of the Andaman Sea.

Day 3 – Koh Tarutao National Park

At 8 Mile, visibility opened wide over the pinnacle. Bentstick pipefish hovered above the reef while redbar anthias and juvenile angelfish filled the water column. Fimbriated morays peered from crevices as Spanish mackerel and great barracuda cruised past. The unusual half grouper–half barramundi added a curious highlight (same one as last trip).

Schools of fusiliers, surgeonfish and snappers moved constantly in the current.

A vibrant juvenile Emperor Angelfish with concentric electric blue and white circular patterns swimming near a sea urchin. — Nature’s geometry: The mesmerising circular patterns of a juvenile Emperor Angelfish stand out against the backdrop of a rocky reef.

A large mottled Giant Grouper with its mouth open while a small cleaner wrasse performs its duties on a colourful reef. — Spa day on the reef: A strange-looking Giant Grouper pauses at a cleaning station, allowing cleaner wrasse to attend to it in Koh Tarutao National Park. | Frederique Bechet

Stonehenge brought a quieter atmosphere with a seahorse, Phestilla melanobrachia and flounders resting on the sand, surrounded by wrasses, damsels and butterflyfish moving between soft corals.

At Koh Taru, schools of five-lined snappers dominated the reef, joined by Phestilla melanobrachia and tiger cowries. Fusiliers, goatfish and sweetlips added movement as the light softened towards sunset.

Two pink Skunk Anemonefish hovering above their host anemone with a large intricate sea fan in the background. — A perfect partnership: Skunk Anemonefish find safety among the tentacles of their host, framed by the delicate beauty of a giant sea fan.

A vibrant yellow Tigertail Seahorse with dark markings gripping a branch of pink soft coral. — Master of disguise: A bright yellow Tigertail Seahorse anchors itself to a colourful reef, showing off the incredible camouflage found in Koh Tarutao National Park.

Day 4 – Koh Lanta National Park

Hin Daeng & Hin Muang once again delivered strong currents and active reefs, with schools of trevallies, fusiliers and snappers swirling around the pinnacles, alongside batfish, ghost pipefish, surgeonfish and reef predators patrolling the blue.

At Koh Haa Chimney, the dive shifted back to macro life with Halgerda bacalusia, Cuthona sibogae, Risbecia pulchella and ghostpipefish. Inside the structure, glassfish shimmered while outside, sweetlips, groupers, parrotfish and angelfish filled the reef.

After the dive, we began our overnight crossing towards the Similan Islands, leaving the southern reefs behind.

A close-up of a Risbecia pulchella nudibranch featuring a creamy body with yellow spots and a distinct purple ruffled border. — Elegant patterns: The striking purple edge and delicate spots of a Risbecia pulchella nudibranch found during Day 5 of our expedition in Similan National Park.

A macro image of a Halgerda bacalusia nudibranch featuring a white body with a network of orange-yellow ridges and dark-tipped gills. — Geometry in the blue: The striking ridges of a Halgerda bacalusia captured against the reef. | Renaud Liberge

Day 5 – Similan National Park

West of Eden surprised us with a rare snaggletooth shark, alongside whitetip reef sharks cruising the reef. Pygmy pipehorse hovered delicately while McCosker’s flasher wrasse darted through the water column. The reef revealed a batwing psychedelic seaslug and a perfectly camouflaged devil scorpionfish, surrounded by butterflyfish, surgeonfish, wrasses and schools of fusiliers.

A colourful male McCosker's flasher wrasse displaying vibrant blue, orange and red colours while swimming among smaller reef fish in the deep blue. — Lighting up the reef: A stunning McCosker’s flasher wrasse in full display, a highlight of our dives at Elephant Head Rock.

A macro close-up of a Batwing psychedelic seaslug featuring intricate patterns of purple, orange and green on a soft coral background. — Underwater art: The mind-bending colours and patterns of a Batwing psychedelic seaslug, one of the most unique macro discoveries in the Similan Islands.

At Elephant Head Rock, blue ribbon eels waved from their burrows while octopus moved across the rocks. Three-spot angelfish and a young adult yellow boxfish stood out, while an Andaman jawfish guarded its eggs. Trevallies, snappers and sweetlips completed the dramatic setting.

North Point brought whitetip sharks, a Jenkins whipray and a juvenile Spanish dancer, alongside a wavy sap-sucking seaslug and a passing guitar shark. Schools of fusiliers and snappers added movement.

Two vibrant male Blue Ribbon Eels extending from the same burrow with mouths open against a rocky reef background. — Double the wonder: A rare sighting of two Blue Ribbon Eels sharing a single burrow at Elephant Head Rock.

A large Jenkins' Whipray resting on the sandy seafloor near a rocky outcrop in the clear waters of the Similan Islands. — Resting giant: A Jenkins’ Whipray camouflaged against the sand, a common but always impressive resident of the North Andaman reefs.

At Koh Bon Ridge during sunset, a whitetip reef shark moved repeatedly in and out of the reef, patrolling close to divers in a memorable encounter.

The blackwater dive revealed spear mantis shrimp larvae, squids, pelagic snails, zoea crabs, siphonophores, “pompom tail” shrimp larvae, flatworm larvae, blenny larvae, shrimp larvae, moray eel larvae and larval anemones drifting through the dark. Blackwater once again delivered the surreal, reminding us that some of the ocean’s most fascinating life exists far from the reef.

A transparent ribbon-like larval eel drifting against a pitch-black background during a blackwater dive. — A transparent larval eel drifts through the darkness of the open ocean during the blackwater dive.

A small transparent juvenile squid with visible internal organs and orange pigment spots. — A delicate juvenile squid reveals its translucent body while drifting through the blackwater.

A delicate translucent blue sea butterfly shell drifting in the open ocean at night. — A tiny sea butterfly drifts through the open ocean during the midnight vertical migration.

A highly detailed glass squid with vibrant red and purple chromatophores shimmering against the dark water. — A glass squid reveals its vivid chromatophores against the darkness of the open ocean.

A bell-shaped translucent zoanthid larva floating in the open ocean at night during a blackwater dive. — A translucent zoanthid larva drifts through the open ocean during the blackwater dive.

A translucent larval anemone with long delicate tentacles radiating outward against a black background during a blackwater dive. — A translucent larval anemone drifts through the darkness, one of the many unexpected forms encountered during the blackwater dive.

A translucent Phronima amphipod glowing with blue and gold hues as it drifts through the dark water column. — A translucent Phronima amphipod glows against the darkness of the open water.

From the mesmerising patterns of macro life to the “alien” encounters of the midnight vertical migration, these seven images capture the incredible biodiversity found across our expedition through the Similan and Koh Tarutao National Parks.

Day 6 – Similan National Park

At Koh Bon Bay, orange-spotted glassy bubbles (Hyppo snails) appeared on the reef while a school of batfish gathered in the current alongside giant trevallies and double-spotted queenfish.

A Bowmouth Guitarfish swimming over a rocky reef accompanied by a diverse school of tropical fish in clear blue water. — A prehistoric silhouette: The rare Bowmouth Guitarfish, also known as a Mudray, glides over the reef during an expedition to the Burma Banks.

A large shimmering school of silver Longfin Batfish gathered around a coral pinnacle in the Similan Islands. — Silver symphony: A dense school of Longfin Batfish creates a spectacular wall of silver at the Koh Bon pinnacle.

On Koh Bon West Ridge, an incredible encounter with a bowmouth guitar shark, alongside Spanish dancer eggs, dogtooth tuna and Spanish mackerel hunting in the blue, while fusiliers and surgeonfish filled the reef.

A silhouette of a scuba diver hovering in clear blue water above a large sea anemone hosting a bright orange clownfish. — Exploring the blue: A diver observes the perfect symbiosis between a clownfish and its anemone host in the Andaman Sea.

A large colourful Titan Triggerfish swimming over a hard coral reef under bright sunny surface conditions. — Reef guardian: A Titan Triggerfish cruises over the coral gardens, showcasing the vibrant marine life found in Thailand’s national parks.

Koh Bon Pinnacle was alive with schools of batfish, clown triggerfish, bluefin trevallies, barracudas and yellowback fusiliers.

At Koh Tachai Pinnacle, large schools of barracudas, batfish, giant trevallies, bluefin trevallies and bigeye trevallies dominated the dive, joined by marble groupers and painted spiny lobsters hiding in the rocks.

A large bright pink soft coral blossoming on a rocky reef surrounded by small tropical fish in clear blue water. — A burst of colour: This magnificent pink soft coral is a testament to the healthy, nutrient-rich currents that flow through the Similan Islands.

A dense swirling school of chevron barracuda swimming in the open blue water near the ocean surface. — Power in numbers: A massive school of barracuda creates a shimmering silver wall, a thrilling sight for any diver in the Andaman Sea.

The night dive at Koh Tachai Reef brought hunting behaviour, with schools of checkered snappers and barracudas using our lights to hunt, while giant moray eels swam freely and blacktip sharks cruised the reef.

A Blacktip Reef Shark swimming swiftly over a dark reef at night with its distinctive black-tipped dorsal fin visible against the dark water. — Midnight patrol: A Blacktip Reef Shark cruises the reef edge under the cover of darkness, a prime example of the apex predators encountered during our night dives.

Into the shadows: The sleek silhouette of a Blacktip Reef Shark emerges from the darkness, showcasing the thrilling wildlife sightings possible in the Andaman Sea after sunset.

Day 7 – Surin National Park (Richelieu Rock)

Four dives at Richelieu Rock delivered a spectacular finale. White and yellow ornate ghostpipefish hovered delicately while peacock mantis shrimp and tigertail seahorses added macro highlights.

A macro shot of a spiny Ghost Pipefish hovering near vibrant pink soft corals. — Master of disguise: A Ghost Pipefish blends perfectly with the surrounding soft corals in the Similan Islands.

A close-up of a bright yellow Tigertail Seahorse anchored to the reef substrate. — Golden discovery: A stunning Tigertail Seahorse found tucked away in the rocky crevices of the North Andaman reefs.

Schools of amber jacks, bigeye jacks, longnose emperors, giant trevallies, bluefin trevallies and rainbow runners filled the blue, while juvenile bridled monocle bream, baby octopus, Spanish mackerel and juvenile clown triggerfish added variety. Female Moyer’s dragonet and male Morison’s dragonet completed the scene.

A large swirling bait ball of small silver fish being pursued by several large red snappers in clear blue water. — Eye of the storm: Large snappers dive through a massive bait ball, a spectacular display of predatory action in the Andaman Sea.

A dynamic underwater scene featuring schools of trevally and barracuda silhouetted against the bright surface sun over a coral reef. — The morning rush: Schools of trevally and barracuda congregate at the reef’s edge as the sun breaks through the surface.

Nudibranch diversity was exceptional, including Risbecia pulchella, Chromodoris geometrica, Glossodoris atromarginata, Hypselodoris bullocki, bicolor flabellina, Gymnodoris nigricolor and Glossodoris pallida, while flatworms such as Pseudobiceros sp7 added even more colour.

Around them, dense schools of fusiliers, snappers and glassfish wrapped the pinnacle in constant motion.

A massive dense school of silver jacks swirling in clear blue water over a dark reef edge. — Tornado of silver: A spectacular school of Jacks creates a living vortex in the nutrient-rich waters of the Andaman Sea.

A diverse school of reef fish including snappers and emperors swimming over a lush garden of pink soft corals. — The crown jewel: Intense marine biodiversity flourishes over the iconic pink soft corals of Richelieu Rock.

Day 8 – Similan National Park & Khao Lak Coast

Our final dives brought us back to Koh Tachai Pinnacle, where a hawksbill turtle, schools of batfish, bigeye jacks, barracudas and Spanish mackerel closed the trip with strong pelagic action.

A pair of vibrant yellow and black Raccoon Butterflyfish swimming past a large intricate red gorgonian sea fan on a steep reef wall. — Sunset colours: A pair of Raccoon Butterflyfish, known for their distinct mask-like markings, glide past a massive sea fan in the North Andaman Sea.

A dense circular school of Bigeye Trevally silhouetted against the bright surface sun in deep blue water. — Oceanic vortex: A massive school of Bigeye Trevally creates a shimmering silhouette against the midday sun.

A Kuhl’s Stingray also known as a Bluespotted Maskray resting on the sandy seafloor near soft corals in clear daylight. — Master of the sand: A Kuhl’s Stingray — easily identified by its kite-like shape and blue spotting — rests on the seafloor during a daytime exploration of the reef.

At Boonsung Wreck, a completely different atmosphere awaited. Blue-spotted Kuhl’s rays rested on the sand, honeycomb morays hid within the structure and bentstick pipefish hovered nearby. Schools of fusiliers, snappers, sweetlips and trevallies turned the wreck into a true fish haven.

A large school of Longfin Bannerfish swimming together against a dark reef slope in deep blue water. — Graceful gliders: A school of bannerfish manoeuvres along the reef, their long white dorsal filaments trailing behind them like ribbons in the current.

A vibrant macro shot of a Honeycomb Moray Eel with its mouth slightly open tucked into a colourful coral crevice surrounded by small orange fish. — Pattern perfection: The striking leopard-like markings of a Honeycomb Moray Eel emerge from a vibrant reef corner, a favourite find for underwater photographers.

We then returned to Tap Lamu Pier in Khao Lak, saying goodbye after another rich and diverse journey through the Andaman Sea.

From limestone reefs to offshore pinnacles, this journey captured the changing rhythm of the Andaman Sea — where each dive revealed a new balance between movement, colour and hidden detail.

Until the next tide brings us together again — dive well, dive aware, and see you soon, fellow divers.

A vibrant orange sun setting over the calm ocean and distant islands viewed from the deck of a dive boat. — Golden hour at sea: The sun dips below the horizon, painting the sky in hues of pink and orange — the perfect end to another day of exploration in Thailand’s national parks.

Photos by: Franck Fogarolo, Frederique Bechet and Renaud Liberge

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Camille Rovillain

Camille’s love for travel and diving began in her mid-twenties, taking her across oceans and continents before she finally settled in Thailand. In 2012, she co-founded The Smiling Seahorse, driven by a desire to explore and share some of Southeast Asia’s most remote and unexplored dive destinations. A proud mother of two, Camille still hops on board The Smiling Seahorse every month. Passionate about macro life, she delights in guiding fellow enthusiasts on unforgettable dives across the Andaman Sea — from Myanmar’s Mergui Archipelago all the way to Thailand’s Malaysian border.

One Response

Andrew Eade says:

August 31, 2026 at 4:32 am

What a fabulous trip this was! Great account of the wonderful things we saw…. Thank you Camille and the Smiling Seahorse team!

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Trip report | Thailand | South & North Andaman Expedition, 29th March – 5th April 2026