Five Islands Koh Samui (Koh Si Koh Ha): Limestone Cliffs, Swiftlet Nests and How to See Them

Sail along Koh Samui’s south-west coast and you will see a cluster of steep, jungle-topped rocks rising straight out of the sea off Taling Ngam. These are the Five Islands, known in Thai as Koh Si Koh Ha, which translates literally as “four islands, five islands”. There are no beach bars and no landing jetty for visitors, and that is deliberate. The cliffs are home to swiftlet colonies whose nests rank among the most valuable natural products in Asia.

Below we explain what you are looking at and why Five Islands Koh Samui boat trips view the cliffs from the water. You will also find how to get the most out of a visit, including where to stand on deck and what to bring.

Quick facts

Thai name	Koh Si Koh Ha (เกาะสี่เกาะห้า), “four islands, five islands”
Location	Off the Taling Ngam coast, south-west Koh Samui, Surat Thani province
What they are	Small, steep limestone islets with sheer cliffs and caves
Famous for	Colonies of swiftlets that build edible nests from their saliva
Can you land?	No. The islands and the swiftlet nests are viewed from the boat. Guests do not land or collect nests
How to visit	On a boat trip that passes the islands, such as the Samui Journey 1-Day Catamaran (arrives about 11:20 AM)
Best light	Late morning to early afternoon for colour in the water, early morning for soft side-light
Not to be confused with	Ko Si Ko Ha in Songkhla Lake, Phatthalung province, a different and larger nest-island group

Why “four islands, five islands”?

The name is a riddle you can solve from the boat. From most angles one of the islets hides behind another, so you count four. Move along a bit and the fifth appears. Watch for it as the boat approaches. Children usually enjoy spotting it.

If you are searching online, be aware there is another, better-documented Ko Si Ko Ha in Songkhla Lake (Phatthalung province), a well-known nest-harvesting site far to the south on the mainland. Many Thai-language results are about that one. The Samui group is much smaller and sits in the open Gulf of Thailand.

The limestone: what you are looking at

The Five Islands are limestone, the same family of rock as the far larger Mu Ko Ang Thong National Marine Park to the north-west. Rainwater dissolves limestone slowly and waves undercut it, so you will see:

• Sheer, almost vertical walls coming up from deep water.
• Overhangs and notches at the waterline, where the sea has eaten into the foot of the cliff.
• Dark cave openings and cracks higher up. These shaded, sheltered spots are what swiftlets need.
• Vegetation clinging to the tops, where a thin layer of soil has built up.

From the deck you can fit the full height of the cliffs into one frame, which is why these islands photograph so well.

Swiftlets and the edible-nest trade

The birds

Swiftlets are small, fast birds that spend most of the day in the air catching insects. Several species in Southeast Asia, including the edible-nest swiftlet (Aerodramus fuciphagus), nest in colonies in limestone caves and on cliff faces. They can even navigate in darkness using echolocation, a rattling call that lets them find their nests deep inside caves.

The nests

The nests are made almost entirely of hardened saliva, stuck to the rock as a small bracket. A typical nest is only around 6 cm across and weighs roughly 14 g. Once cleaned, the nests go into bird’s nest soup, a delicacy prized in Chinese cooking for centuries, and they sell for very high prices.

Why the islands are guarded

Because the nests are worth so much, collection in Thailand runs on a state concession system, with rights granted to licensed operators. Nest sites are usually watched to deter poaching. So for visitors it is straightforward. You look from the water. You do not land or climb.

Heavy harvesting has hurt swiftlet populations in parts of Asia, so keeping a respectful distance helps the colonies too. Do not shout, fly drones close to the cliffs or do anything else that might disturb nesting birds.

How to see the Five Islands from Koh Samui

On the Samui Journey 1-Day Catamaran

The Five Islands are the first stop of the day. After hotel pickup between 9:00 and 9:40 AM, guests board at Bang Kao Pier and the catamaran leaves at about 10:30 AM, reaching the Five Islands at around 11:20 AM. The visit is viewing only. The boat cruises near the cliffs so guests can see the rock formations and the swiftlet nesting areas, then carries on to Koh Tan at around 11:50 AM for snorkelling. Lunch is served onboard, and Pig Island follows in the afternoon.

A large, stable catamaran is a comfortable boat for this kind of sightseeing. There is room on the upper deck to move around for photos, shade if you want it, and a toilet onboard.

By private longtail or speedboat

Hotels and boat operators along the Taling Ngam and Thong Krut coast can also arrange private trips past the islands. If you go this way, agree in advance that the boatman will stay on the water. Ask what other stops are included too, because the Five Islands on their own are a short sightseeing visit.

From the shore

You can see the islands from parts of the Taling Ngam coastline. That is fine for spotting them, but from that far away you will not make out the cliff detail or nesting areas.

Five Islands Koh Samui photo tips from the deck

• Go up to the upper deck early as the boat approaches, so you are in place before everyone else moves.
• Use the zoom. The nesting areas are high on the rock, and a 2–5x phone zoom or a telephoto lens makes a big difference.
• Wait for the “four becomes five” moment and take a short burst as the hidden islet comes into view.
• Polarising filter or sunglasses trick. A polariser (or shooting through polarised sunglasses on a phone) cuts glare and deepens the colour of the water.
• Include a person or the boat rail for scale. The cliffs look smaller in photos than in real life.
• Keep drones away from the cliffs. Flying near nesting birds can disturb them, and Thailand has its own drone registration rules, so check those before you fly anywhere.

When to go

Most Five Islands Koh Samui tours are part of a south-coast boat trip, so the same seasonal advice applies. Koh Samui’s heaviest rain normally falls from mid-October to early December, when seas can be rougher and trips may be rescheduled. The rest of the year is generally better for a boat day, though conditions can change quickly in any season.

On Samui Journey trips, if the sea is unsafe you are offered another date free of charge, and a full refund if the new date is also affected.

What to bring

• Binoculars. A compact pair is enough for picking out nests and birds on the cliffs.
• Phone or camera with zoom, plus a dry bag or waterproof pouch.
• Sun protection. Hat, sunglasses and reef-safe sunscreen for the swim at Koh Tan later.
• Light cover-up for the sail, as it can be breezy on the upper deck.
• Swimwear under your clothes, so you are ready to go in when the boat reaches Koh Tan.

Good to know

• It is a sightseeing stop, not a beach stop. Save your swimming and snorkelling for Koh Tan.
• There is nothing to buy at the islands. Drinks and lunch on the catamaran are included.
• Respect the birds and the workers. The islands are a working site as well as a wildlife habitat.
• Seasickness. If you are prone to it, take medication before departure and sit on the lower deck, near the middle of the boat, where there is least movement.
• Combining days. For a slower day on land after a full day at sea, the 3-hour morning or afternoon programme at Samui Elephant Kingdom fits in easily, and you can see more of Samui’s rock formations at Hin Ta and Hin Yai.

FAQ