- The Emerald Lake (Talay Nai) sits inside Mae Ko island and you see it from a viewpoint at the top of a short, steep staircase.
- Swimming in the lake is not allowed, so plan your swim for the beach or the water around the boat.
- The park fee is ฿300 per adult and ฿150 per child (children aged 12 and older pay as adults), and it is not included in the boat price.
- Ang Thong is usually closed every year from 1 November to 15 December, so no trips to the lake run in those weeks.
- Private 8-hour Ang Thong charters run from ฿32,000 on Anda, and Pearl costs ฿39,000 with hotel transfer included.
The engines go quiet off Mae Ko, the water is flat, and someone on deck asks whether the climb is really worth leaving the shade. It is. The view in all those Emerald Lake Ang Thong photos costs you one short, steep walk and a little good timing, and on a private boat you get to choose the timing.
This guide covers the part most trip descriptions skip: what the walk feels like, what to put on your feet, why nobody is swimming down there, and how to fit it into a day at sea without rushing the rest.
What is the Emerald Lake Ang Thong visitors climb to see?
It is a saltwater lagoon in the middle of Mae Ko island, surrounded by limestone walls and jungle. Thai people call it Talay Nai, which means "inner sea", and you look down on it from a viewpoint rather than walk up to its shore.
The name is honest about the colour. On a bright day the water turns a milky green that looks unreal against the grey rock. The lake is fed by the sea through channels under the limestone, so it is salt water that rises and falls with the tide, not a freshwater pool.
Mae Ko is one of the main islands of Mu Ko Ang Thong National Park, the group of 42 islands west of Koh Samui. It is also the stop that nearly every boat in the park wants to make, which is why timing matters more here than anywhere else on the route.
My honest view: it is the one short walk in the park that almost everybody should do. It is far easier than the big viewpoint on Wua Talap, it takes little time, and the picture you get at the top is the one you came for. If your day allows only one walk, make it this one.
How hard is the walk up to the lake?
It is short but steep: a staircase with handrails, climbing through the forest from the beach to the viewing platform. Most reasonably fit people manage it easily, and the whole visit usually takes under an hour with time for photos and for catching your breath.
The stairs are the tiring part, not the distance. It is hot and still in the trees, with little breeze, and the steps can be narrow. On a busy day people come up and down the same path, so you will sometimes wait while a group squeezes past.
Most healthy children who like a climb will be fine with a hand to hold on the steep bits, but toddlers usually have to be carried. People with bad knees, heart trouble or balance problems should think it over honestly. Going down is harder on the knees than going up.
Nobody has to go. If someone in your group would rather stay, they can sit on the sand or on the boat and lose nothing but the view. That is one of the small pleasures of a private charter: the boat waits for your group, and no one is hurried along by a tour leader's flag.
Why can't you swim in the Emerald Lake?
Swimming is not allowed, because the lake is a protected and fragile part of the national park. Treat it as a place to look at, not a place to get into, and tell the kids before the climb so nobody arrives at the top in tears.
There is also a practical reason. The walls around the lagoon are sheer, sharp limestone, there is no beach down there, and the walkway stops at the viewing platforms. Even without the rule it would be a bad place for a dip.
Some older blogs and photos suggest otherwise, and rules in national parks can change, so listen to the rangers and the guide on the day. Please don't try to climb over anything for a better photo. The rangers take this seriously, and the rock will cut you long before they reach you.
The good news is that the water around Mae Ko and the rest of the park is warm, and you will be in it within the hour. Put your swimsuit on under your clothes in the morning and plan to swim straight after coming back down, when you will want it most.
What should you wear on your feet?
Wear sandals with a back strap or light trainers that can get wet. Footwear matters more than anything else you pack for this stop, because you step off the boat in wet sand and then climb stairs with damp feet.
Flip-flops are the classic mistake. People do climb in them, but they slip on wet steps and are awkward on the way down. Going barefoot on hot, rough steps is worse. Here is what I would tell a friend to bring on the walk:
- Strap sandals or water shoes, dry enough to grip and tough enough for a few wet landings.
- A small bottle of water, because the climb is hotter than it looks from the boat.
- A dry bag or a plastic bag for your phone on the way to the beach.
- A hat and a light shirt over your swimsuit, as the stairs are partly in the sun and you will want the cover.
- Some cash in Thai baht, kept dry and easy to reach.
Leave the big beach bag, the speaker and the towels on board. The less you carry up the stairs, the more you will enjoy them, and on a private boat nobody else is sharing the deck with your things.
When is the best time to see the Emerald Lake?
Go when the sun is high enough to light the water and the big group boats are not on the island. The colour needs direct sun, and the quiet needs you to be off the usual tour rhythm, so the best plan is usually to ask the captain to land at Mae Ko either earlier or later than the crowd.
Large group tours tend to reach the island around the middle of the day. On a private boat you are free to swap the order of your stops, and the crew knows the park and sees how busy it is on the day. Tell them at the start that the lake matters most to you and let them work out the order.
Cloud changes the picture more than people expect. Under grey skies the lake looks dull and flat, and a shower can make the steps slippery. It is worth being flexible for an hour if the sky looks like it will clear.
The seasons matter too, and these are the dates to check before you plan anything:
| Period | What to expect at the lake |
|---|---|
| 1 November to 15 December | The park is usually closed every year, so no Ang Thong trips run |
| Rest of December and January | The north-east monsoon can still make the sea rough, and trips may change route or be postponed |
| From about February | Calmer seas return in most years, and this is a good time to plan the day |
| Middle of the year | Usually a good time too, with short showers possible, so stay flexible |
For a wider look at the months, read this month-by-month guide to boat trips on Koh Samui. Weather here never reads the calendar, so a manager will confirm the conditions for your date.
How do you combine the lake with the viewpoint and the beaches?
A sensible day has three parts: the lake on Mae Ko, a swim and snorkel, and a long beach stop on Wua Talap, with the viewpoint there only if your group really wants it. An 8-hour charter gives you time for one hard climb and one easy climb, but few people enjoy doing both.
The viewpoint on Wua Talap is a different animal from the lake walk. It is a long, tough climb over sharp limestone, with ropes in places, and it is really only for fit people in proper shoes who are starting well before the hottest part of the day. The view over the islands is the best in the park, but it costs far more sweat. Rangers may restrict the trail, so check on the day.
My opinion: unless you are keen hikers, skip the big viewpoint and take the extra time in the water. A tired, overheated group is not what you paid for. The lake gives you the postcard shot for a fraction of the effort.
Here is how a relaxed day can run, in an order the captain can change to suit the sea and the crowds:
- Pickup, then the crossing from Koh Samui to the park.
- Mae Ko: the beach, the stairs and the lake, then a swim to cool down.
- A snorkel stop in a sheltered spot chosen by the crew on the day.
- Lunch, if you have arranged it, and a long beach stop on Wua Talap.
- A slow look at the rock shapes on the way out, then the crossing home.
The Ang Thong yacht charter page shows the boats that run this route. The earlier guide to Ang Thong routes and timing by private boat goes deeper on the whole park if the lake is only one part of your plan.
Which boat suits an Emerald Lake day?
For most small groups the answer is Pearl: ฿39,000 for the whole boat for 8 hours, for up to 6 guests, with hotel transfer included. Extra guests are ฿2,000 each, up to 15, and Pearl's 38-foot speedboat is the one guests book most often.
All these prices are for the boat, not per person. The park fee of ฿300 per adult and ฿150 per child (children aged 12 and older pay as adults) comes on top on every boat, and lunch is usually extra on speedboats. Here are the nine speedboats side by side for the Ang Thong route:
| Boat | Ang Thong, 8 hours | Price covers | Each extra guest | Maximum guests | Hotel transfer |
|---|---|---|---|---|---|
| Anda | ฿32,000 | Up to 6 | ฿1,000 | 12 | Included |
| Pearl | ฿39,000 | Up to 6 | ฿2,000 | 15 | Included |
| Ruby 38 | ฿44,000 | Up to 6 | ฿2,000 | 8 | Included |
| Ofcourse | ฿44,000 | Up to 6 | ฿1,000 | 24 | Not included |
| Sapphire | ฿44,000 | Up to 6 | ฿1,000 | 24 | Not included |
| Ti Ti | ฿44,000 | Up to 6 | ฿1,000 | 24 | Not included |
| Neverland | ฿51,000 | Up to 10 | ฿1,000 | 37 | Not included |
| Summer Casa | ฿56,000 | 2 people | ฿2,000 | 10 | Ask, leaves from the Naval Base |
| Coco Cay | ฿56,000 | 2 people | ฿2,000 | 10 | Ask, leaves from the Naval Base |
Pearl is the easy choice for most groups, Anda is the lowest price on this route for a group that wants a simple day, and Ruby 38 suits a small party of up to 8 who like a sporty boat.
Ofcourse, Sapphire and Ti Ti are the same kind of 300 hp boat with room for 24, so choose them for a bigger group and arrange your own way to the pier; Neverland, with 10 guests in its base price and space for 37, is the one for a real crowd.
Couples should look at Summer Casa and Coco Cay. They are priced for 2 people and come with a butler, a beach picnic, a paddle board, a sun bed and an onboard toilet, which is a real comfort on a long day.
Who should choose something else? Anyone who dreads a bumpy crossing. Speedboats are quick, but you feel the waves, so people prone to seasickness, older guests or families with small children may be happier on a catamaran, such as Nina, at ฿65,000 for a 10-hour day. It is slower, so you will have less time at each stop, but it is much gentler on the stomach.
What to sort out before your Emerald Lake day
A little preparation makes this an easy stop. The date is the first thing to check, because no trips run during the yearly closure, and the sea can change plans around it.
- Pick a date outside 1 November to 15 December, and keep a spare day if you are coming in the monsoon months.
- Budget for the park fee, as it is not part of the boat price, and ask the manager how it is paid.
- Tell the manager when you book that the lake is your priority, and mention anyone in the group who cannot manage stairs.
- Ask about lunch at the same time, since it is an extra on most speedboats.
- Take a seasickness tablet before the crossing if you are prone to it, not once you already feel bad.
To book, choose a boat and send the request on its page, or write on WhatsApp. The request is free and non-binding, and a manager confirms that the boat is available and tells you the final price for your group.
Questions and answers
Is the Emerald Lake the same as the Blue Lagoon in Ang Thong?
People use several names for it. Talay Nai, Emerald Lake, Blue Lagoon and Inner Sea usually all mean the same lagoon on Mae Ko. If in doubt, ask for Talay Nai on Mae Ko and the crew will know exactly what you mean.
Is the park fee included in a private charter?
No. The Ang Thong park fee is ฿300 per adult and ฿150 per child, and children aged 12 and older pay as adults. It comes on top of the boat price and is paid separately.
Can kids do the walk up to the lake?
Most children who enjoy a climb can manage it with an adult beside them, though the stairs are steep. Toddlers usually have to be carried, which is hard work in the heat. A parent can always stay on the beach with the little ones while the rest go up.
Can you visit the Emerald Lake without going on a boat tour?
No, Mae Ko can only be reached by boat, so you need a tour or a charter. A private charter has the advantage of letting you choose when you land. That makes it easier to avoid the busiest part of the day.
Can you go to Ang Thong in November?
The park is usually closed every year from 1 November to 15 December, so no Ang Thong trips run then. From about November to January the north-east monsoon can also make the sea rough, and trips may change route or be postponed. Koh Samui's nearer islands can still be possible in good weather, so ask about the options for your date.
How long is the day on a speedboat to Ang Thong?
The Ang Thong route on the speedboats listed here is an 8-hour charter. That is enough for the lake, a swim, a snorkel stop and a beach, but not much more without feeling rushed. The sea on the day can change how long the crossing takes.
Is the walk worth it if the sky is cloudy?
Still yes, though the colour will be less intense than in the photos. The view of the lagoon inside its limestone walls is impressive in any light. Ask the captain if there is a chance of clearer sky later, and adjust the order of the stops if the plan allows.
Ready to choose your boat?
Every boat page shows the routes, prices and what is included. The booking request is free: a manager checks the boat is free on your date and confirms the price.
Updated 14 November 2026. Prices can change: the boat page always shows the current price.
