Koh Bon is the Similan Islands' own answer to the manta ray encounter, an isolated granite island sitting apart from the park's main chain, built around a wall and ridge system that has become one of the most consistent places in Thailand to watch these animals up close. Where Richelieu Rock and Hin Daeng and Hin Muang both offer manta possibilities alongside a broader mix of marine life, Koh Bon is more specifically a manta-focused site, and divers who plan a Similan Islands liveaboard around this one particular encounter tend to know exactly what they're hoping for before they ever get in the water.

That focus doesn't make Koh Bon a one-trick site. The island's underwater topography, a dramatic wall dropping into genuinely deep water alongside a shallower ridge extending out from the island itself, offers two distinct dive profiles within the same location, and the site rewards repeat visits across a longer liveaboard stay in a way that makes it a genuine highlight rather than a single quick stop on a broader itinerary.

Where Koh Bon sits and how to reach it

Koh Bon lies northwest of the main Similan Islands chain, separated enough from the park's core numbered islands that it functions almost as its own destination within a broader Similan Islands itinerary rather than one stop among many closely clustered sites. Nearly all access comes via liveaboard, since the island's position makes it a genuinely awkward day-trip destination from Khao Lak given the additional distance beyond the core park boundary, though a small number of longer, dedicated day trips do run here during peak season for divers without the time for a multi-day liveaboard.

Because of this relative isolation, Koh Bon tends to feature as a deliberate, planned stop on a liveaboard itinerary rather than an incidental one, and operators running longer, four-day-plus itineraries are generally more likely to include multiple passes at the site than those running shorter, three-day trips focused more tightly on the park's core islands.

The ridge and the wall

Koh Bon effectively offers two different dives within the same general area, and understanding the distinction matters for setting expectations before you descend. Koh Bon Ridge, the shallower of the two, extends out from the island in a series of granite outcrops and slopes, generally the more reliable location for manta ray sightings given how the site's current patterns tend to concentrate plankton, and by extension manta activity, around this particular structure. Depth here typically runs from the surface down to around twenty metres, making it accessible to a broader range of certification levels than the site's deeper wall section.

Koh Bon Wall, by contrast, is a genuine drop-off, dropping from shallower water down well beyond recreational dive limits, and it's generally dived along its upper sections, typically in the twenty-to-thirty-metre range, rather than followed all the way to its true depth. The wall itself is covered in soft coral and sponges, offering a more conventional wall-diving experience alongside the same manta ray possibility that draws most visitors to the ridge, though sightings here tend to be somewhat less predictable than at the ridge specifically.

The contrast between these two sections is genuinely worth experiencing across the same stop if your itinerary allows, since they offer such different characters despite sitting on the same small island. The ridge feels more open and exposed, a dive built around holding position in current and scanning the blue for movement, while the wall offers the more familiar sensation of a defined vertical feature to follow, coral and sponge-covered rock on one side and open water on the other. Divers who've only experienced one of the two sections often come away with an incomplete picture of what Koh Bon actually offers, and it's worth specifically requesting both if a liveaboard itinerary's schedule allows some flexibility.

Most liveaboard itineraries that include Koh Bon plan to dive both sections across a stop, sometimes on the same day and sometimes across separate visits if the itinerary allows, giving divers the chance to experience both the shallower, more current-active ridge and the deeper, more classically structured wall within a single stay at the site.

What this dive demands

Koh Bon Ridge's current can range from mild to genuinely strong depending on tide, and divers should expect to spend real time holding position in open water while watching for manta activity, a different kind of demand from swimming a route through a reef or boulder formation. Good buoyancy control and comfort maintaining a stable position against current, without resorting to grabbing onto the reef itself, matters considerably here, both for your own air consumption and for the health of the surrounding coral and sponge growth that current-swept ridge formations like this one support.

Reef hooks, a small device that allows a diver to attach temporarily to a bare rock surface without gripping live coral, are used by some operators at current-heavy sites like Koh Bon specifically to let a group hold a stable viewing position without constant finning effort, conserving air and reducing the risk of accidentally drifting into a manta's path. Not every operator uses them, and their use should always be limited to bare rock rather than any living coral surface, but it's worth asking whether your specific trip provides them if you know current is likely to be a factor on the day.

Most operators recommend Advanced Open Water certification for Koh Bon, particularly for the wall section given its greater depth, though the ridge itself is sometimes accessible to strong Open Water divers with adequate experience and a guide willing to keep the group in the shallower sections specifically. As with the other current-exposed sites covered in this guide, it's worth being honest with your operator about your own comfort level with drift conditions before committing to a Koh Bon dive, since the site rewards patience and stability far more than it rewards simply being willing to get in the water regardless of preparation.

The manta encounter itself

Koh Bon's manta rays are drawn to the ridge and wall areas by the same cleaning station dynamic found at other Thai sites with reliable manta activity, small reef fish, generally wrasse species, feeding on parasites and dead skin from the mantas as they slow and circle through the cleaning area. This behaviour means encounters here often extend well beyond a fleeting pass, with mantas sometimes circling a specific section of the ridge repeatedly across a single dive, giving divers genuinely extended viewing time rather than a single brief sighting.

Sightings aren't guaranteed on any specific dive, and conditions, current, season, and simple chance all affect the odds on a given day, but Koh Bon's overall sighting frequency during the core Similan Islands season is considered among the more reliable manta encounters in Thailand, comparable to Hin Muang's own cleaning station further south. Positioning matters considerably for a good encounter: settling into a stable position at a sensible distance from where mantas are actively circling, rather than swimming directly toward an approaching animal, tends to produce longer, calmer encounters, since mantas will readily abandon a cleaning pass if they feel crowded or pursued by an over-eager group of divers.

Group behaviour genuinely affects outcomes at a site like this more than at almost any other type of dive covered in this guide. A group that spreads out, stays low against the ridge, and avoids exhaling large bubble streams directly beneath a circling manta tends to see considerably longer, calmer encounters than a group that clusters together and finning excitedly toward every approaching animal. Experienced guides will typically brief this specifically before the dive, and it's worth taking that briefing seriously even if you've dived manta cleaning stations elsewhere before, since Koh Bon's specific current and topography can make positioning trickier than at calmer sites.

Beyond the mantas

While mantas are Koh Bon's headline draw, the site supports a broader range of marine life worth watching for across a dive. Barracuda schools move through the open water around both the ridge and wall sections, and occasional whale shark sightings, while considerably less predictable than the manta encounters, do occur here during the right conditions, adding a genuine bonus possibility on top of the site's more reliable draw. Leopard sharks make occasional appearances resting on sandy patches near the base of the wall, and the wall's soft coral and sponge coverage supports a reasonable variety of reef fish and smaller macro subjects for divers who take time between current-driven sections to look closely at the formation itself.

Turtles pass through the site's calmer sections periodically, and the granite structure itself, similar in character to the boulder formations found throughout the broader Similan Islands, offers enough textural interest that a Koh Bon dive rarely feels one-dimensional even on days when manta activity is quiet. It's worth genuinely embracing this broader marine life on a day when mantas don't show, rather than treating the dive as a disappointment purely because the headline encounter didn't happen, since the site's underlying reef and wall diving holds up well entirely on its own merits.

Photography at Koh Bon

Wide-angle and fisheye setups are the clear choice for most divers visiting Koh Bon, given how much of the site's appeal centres on the possibility of a large, open-water subject passing through frame. Positioning yourself with the ridge or wall as a background element, rather than shooting purely into open blue water, tends to produce more compelling images of any manta encounter, giving the shot a sense of place and scale that a manta photographed against featureless blue water often lacks.

Because current at the ridge specifically can make holding a stable camera position genuinely challenging, it's worth practising careful buoyancy and positioning technique at calmer sites before attempting serious photography here, since a photographer who's constantly correcting position against current will generally produce blurrier, less considered images than one who's found a stable, current-sheltered spot to work from.

How Koh Bon compares to other manta sites

Divers weighing up Koh Bon against Hin Muang's own cleaning station further south, covered in detail elsewhere in this guide, are choosing between two genuinely comparable manta encounters with somewhat different overall character. Koh Bon's current tends to be marginally more predictable and consistent than Hin Muang's, making it a slightly more approachable introduction to this style of pelagic-focused diving for divers newer to current-driven sites, while Hin Muang's setting within the more current-intense Hin Daeng and Hin Muang pairing offers a broader mix of marine life and topography alongside its own manta possibility. Divers with time to visit both across a longer Thailand trip often find comparing the two directly, rather than relying on secondhand accounts, genuinely worthwhile, since the differences in current character and overall feel are more noticeable in person than any written description fully captures.

Compared to Richelieu Rock's more balanced mix of macro density and occasional pelagic activity, Koh Bon is a considerably more specialised site, built almost entirely around the manta encounter rather than offering the same breadth of smaller subjects. Divers with limited time who have to choose should think honestly about what they're prioritising: Koh Bon for the most focused, dedicated manta experience within the Similan Islands specifically, or Richelieu Rock for a broader overall dive that happens to include real pelagic potential alongside its other strengths.

Planning a Koh Bon visit

Given how strongly Koh Bon's reputation rests on its manta encounters, it's worth confirming directly with your liveaboard operator how many separate dives at the site are included in a given itinerary, since a single quick stop offers considerably lower odds of a strong encounter than two or three dives spread across different current conditions and times of day. Longer liveaboards, generally four days or more, are more likely to build in this kind of repeat access than shorter three-day trips focused more broadly across the whole Similan Islands chain.

It's also worth asking your dive guide about recent manta activity at the site before your specific dive, since local knowledge of where and when mantas have recently been active can meaningfully improve a guide's ability to position the group for a genuine encounter rather than simply hoping for good luck. Some liveaboard crews maintain informal logs of recent sightings across their trips, and a guide willing to share that recent history with you before the dive is generally a good sign of an operator taking the site seriously rather than treating it as a routine stop.

Common questions about Koh Bon

What's the difference between Koh Bon Ridge and Koh Bon Wall? The ridge is shallower, generally offers more reliable manta sightings, and suits a broader range of certification levels, while the wall is deeper, offers a more classic wall-diving profile, and tends to have somewhat less predictable manta activity.

Are manta sightings guaranteed here? No, though Koh Bon's overall sighting frequency during the core season is among the more reliable in Thailand, comparable to Hin Muang's cleaning station further south. No responsible operator will promise an encounter on a specific dive.

Do I need Advanced Open Water to dive Koh Bon? It's recommended, particularly for the wall section, though the shallower ridge is sometimes accessible to strong Open Water divers with sufficient experience and appropriate guiding.

How many dives should I plan here to see a manta? Two or three separate dives, ideally across different times of day or tide conditions, meaningfully improve your odds compared to a single quick stop, and it's worth prioritising an itinerary that allows this kind of repeat access if a manta encounter is your main reason for visiting.

Koh Tachai carries a different kind of story than most of the other sites covered in this series, one that says as much about how Thailand manages its marine parks as it does about the diving itself. The island, sitting north of the main Similan Islands chain, was closed to visitors entirely for several years after years of heavy tourist traffic left its reef systems under genuine strain, and its eventual reopening came with considerably stricter visitor limits than existed before the closure. That history has left Koh Tachai with a reputation among divers as one of the wilder, less trafficked sites accessible from this stretch of the Andaman coast, a place that feels noticeably different from the busier core Similan Islands sites even though it sits within easy reach of the same liveaboard itineraries.

Beyond that history, Koh Tachai is genuinely worth diving on its own underwater merits: strong current supporting large schools of fish, a sloping reef and pinnacle structure that rewards divers comfortable with drift conditions, and a real, if unpredictable, chance of manta ray or whale shark activity passing through open water nearby.

The closure, and why it matters

Koh Tachai's closure, which ran for a meaningful stretch of years before the site reopened under new management rules, came in response to visible reef damage linked directly to the sheer volume of divers and snorkellers visiting during the site's peak popularity. Thailand's national parks department made the decision to close the island entirely, giving the reef systems time to recover without the constant pressure of daily tourist boats, anchoring, and diver contact. This wasn't an isolated decision either; it reflected a broader recognition across several of Thailand's marine parks during this period that some of the country's most popular sites were being loved to the point of genuine damage, a pattern echoed at other locations covered elsewhere in this guide, including the more widely publicised closure of Maya Bay near Koh Phi Phi.

When Koh Tachai reopened, it did so with a considerably more limited visitor capacity than before, along with stricter rules around anchoring and group sizes designed specifically to prevent a repeat of the damage that led to the original closure. Mooring buoys replaced anchoring directly onto the reef in many cases, and the total number of boats and divers permitted at the site on any given day was capped well below pre-closure levels. For divers today, this means Koh Tachai generally feels less crowded than several of the more heavily trafficked core Similan Islands sites, a direct and intentional consequence of the management changes put in place, and it's worth understanding this history as context for why the site carries the particular reputation it does among divers who know the broader story rather than simply showing up for a day of diving.

Where Koh Tachai sits and how to reach it

Koh Tachai lies north of the main Similan Islands chain, closer to the Surin Islands than to the Similans' core numbered islands, and it typically features on liveaboard itineraries that combine both national parks across a longer multi-day trip rather than on shorter excursions focused purely on one park or the other. Given the site's more limited visitor capacity following its reopening, it's worth confirming directly with a liveaboard operator that a specific itinerary actually includes a Koh Tachai stop, since not every trip covers it, particularly shorter departures prioritising the more central sites within either park.

Day trips to Koh Tachai are rare given the island's distance from any mainland departure point, and a liveaboard covering both the Similan and Surin Islands, or specifically routed to include this northern stretch of coast, remains the standard way most divers reach the site.

The dive itself

Koh Tachai's underwater topography centres on a sloping reef and pinnacle structure, with granite boulders and reef sections extending from shallower water down to greater depth, broadly similar in character to formations found throughout the wider Similan Islands chain but generally less explored given the site's lower overall visitor volume. Current here can run genuinely strong, a direct consequence of the island's exposed position, and it's this current that supports the dense schooling fish activity the site has become known for.

Divers should expect a drift-style dive profile at Koh Tachai more often than a fixed circuit, with guides typically planning entry and exit points around expected current direction rather than following a rigid predetermined route. This makes the site considerably more demanding than some of the calmer, more sheltered reef dives found closer to the main Similan Islands, and most operators recommend Advanced Open Water certification with genuine current experience before including a guest on this particular stop.

What this dive demands

Comfort with drift diving matters more at Koh Tachai than at almost any other site covered in this guide's Similan Islands coverage, given how consistently current shapes the actual experience here rather than being an occasional factor. Divers should be genuinely comfortable maintaining position and orientation while moving with current, rather than fighting against it, and a properly deployed surface marker buoy is effectively essential given the open, exposed nature of the site and the real possibility of drifting some distance from the boat across a single dive. Boat crews here typically track diver bubbles and surface markers closely throughout a dive, and it's worth listening carefully to any specific pickup procedure covered in the pre-dive briefing, since drift profiles at exposed sites like this genuinely do require more active tracking than a fixed-route dive at a sheltered reef.

Because Koh Tachai's visitor numbers remain deliberately limited following its reopening, groups here also tend to be smaller than at the busier core Similan Islands sites, which in practice means less crowding underwater but also less room for a guide to closely manage a large, mixed-ability group. It's worth being honest about your own current experience before booking, since this isn't a site well suited to divers still building confidence with drift conditions.

Marine life at Koh Tachai

The strong current running through Koh Tachai supports genuinely large schools of fish, including barracuda and various species of trevally and fusilier, moving through the site's open water sections in dense, shifting formations that make for striking wide-angle viewing even without a larger pelagic encounter. Manta rays and, less predictably, whale sharks do pass through the area, drawn by the same current-driven plankton activity that supports the site's smaller fish schools, though sightings here are considerably less reliable than at dedicated cleaning station sites like Koh Bon or Hin Muang.

Leopard sharks make occasional appearances resting on the site's sandy patches, and the reduced visitor pressure since Koh Tachai's reopening has, by most accounts, allowed both coral coverage and general fish density to recover meaningfully compared to the site's condition before its closure, giving divers today a genuinely healthier reef experience than existed during the years leading up to the shutdown. Giant grouper and various species of trevally patrol the deeper sections of the reef slope, generally unbothered by the smaller groups of divers now visiting under the site's revised capacity limits, and the overall sense many repeat visitors report is of a reef that's genuinely rebuilding its confidence, with fish behaving with less wariness around divers than at more consistently crowded sites elsewhere in the region.

Photography considerations

Koh Tachai's strong current makes it a considerably more demanding photography site than several of the calmer sites covered elsewhere in this guide, and wide-angle setups suited to capturing schooling fish activity in open water tend to work better here than macro configurations that require sustained, stable positioning against current. Photographers should expect to spend more energy simply managing position and buoyancy here than at gentler sites, and it's worth prioritising a stable, low-drag camera rig over anything bulky or difficult to manage one-handed while also controlling your own drift. A rig with excessive drag or awkward buoyancy tends to become a genuine liability in the kind of current typical here, pulling a photographer off balance at exactly the moment a good shot presents itself, so streamlining equipment specifically for this site is worth the extra preparation for anyone planning to shoot seriously.

How Koh Tachai compares to nearby sites

Divers who've already covered the Similan Islands' core sites, or Koh Bon specifically, often find Koh Tachai offers a genuinely different character: less predictable in terms of headline pelagic encounters, but considerably wilder and less crowded given its more limited visitor capacity. Where Koh Bon's manta cleaning station offers a fairly reliable, specific encounter to plan a dive around, Koh Tachai's appeal is more about the overall intensity of current-driven fish activity and the site's relatively untouched feel following its extended closure.

This difference in character means the two sites suit somewhat different priorities. Divers specifically chasing a manta ray encounter with the best possible odds should generally prioritise Koh Bon or Hin Muang over Koh Tachai, while divers who've already had strong pelagic encounters elsewhere and want a genuinely different kind of dive, current-driven, schooling-fish focused, and noticeably quieter in terms of other dive groups, tend to rate Koh Tachai as one of the more memorable stops on a longer Similan and Surin Islands liveaboard specifically because it doesn't try to replicate what those other sites already offer.

For divers who've found the busier core Similan Islands sites more crowded than they'd hoped, Koh Tachai offers a genuine alternative within the same broader park system, trading some predictability in marine life encounters for a noticeably quieter, less trafficked diving experience.

Planning a Koh Tachai visit

Given the site's more limited visitor capacity, it's worth booking a liveaboard specifically confirmed to include Koh Tachai well in advance, rather than assuming any Similan or Surin Islands itinerary automatically covers it. Longer liveaboards combining both national parks across four days or more are generally the most reliable way to include this stop, and it's worth discussing current conditions and expected drift patterns with your operator ahead of the dive itself, given how central current is to the overall experience here.

Because visitor numbers are capped, it's also worth asking directly whether your specific operator holds a confirmed allocation for the site on your planned dates, since the more limited capacity following the site's reopening means demand can occasionally outstrip availability during the busiest weeks of peak season. A guide with genuine, regular experience at Koh Tachai specifically, rather than one simply familiar with the broader Similan Islands, will generally offer a noticeably better briefing on current conditions and expected fish activity, given how much local, site-specific knowledge matters at a location this dependent on drift conditions.

Common questions about Koh Tachai

Why was Koh Tachai closed, and is it safe to dive now? The site closed for several years to allow reef recovery following damage linked to heavy visitor traffic, and it reopened with stricter visitor limits designed to prevent a repeat of that pressure. It's fully open to diving today under these new management rules, and the site's reef systems have shown genuine recovery in the years since reopening.

Do I need Advanced Open Water to dive here? Yes, in practical terms. Most operators require it given the genuine current conditions typical of this site, and divers without solid drift diving experience should build that skill at gentler sites first rather than treating Koh Tachai as a place to gain that experience.

Are manta ray or whale shark sightings reliable here? No, considerably less so than at dedicated cleaning station sites like Koh Bon or Hin Muang. Sightings do occur but are less predictable, and the site's main draw is its overall current-driven fish activity rather than a single specific pelagic encounter.

Can I visit Koh Tachai as a day trip? It's rare given the island's distance from mainland departure points. A liveaboard covering the Similan and Surin Islands, or specifically routed through this stretch of coast, remains the standard way to reach it, and it's worth confirming a specific itinerary includes the stop before booking.