Dive Site: Koh Bon — West Ridge

About Koh Bon — West Ridge

Koh Bon West Ridge, nestled in Thailand's Similan National Park, is a renowned dive site celebrated for its stunning topography and abundant marine life. This uninhabited limestone island, approximately 20 kilometers northwest of the main Similan group, features a horseshoe shape with a distinctive hole cut through by strong waves. The West Ridge itself extends out from the western side of the island. Visible are impressive rock formations, sheer walls, and a variety of colorful soft corals, some forming unique mushroom-shaped bommies and sea fans that sway with the current. The general underwater scenery is well-preserved. It is a cleaning station for manta rays, especially during January to April, when they come to feed on plankton and be cleaned by smaller reef fish. Other frequent sightings include barracudas, tunas, groupers, eagle rays, stingrays, leopard sharks, and various reef fish and invertebrates. The West Ridge features a steep, coral-covered slope on its western side and a dramatic wall on its northern side, both descending to significant depths. While the ridge offers shelter for macrolife like nudibranchs, moray eels, and shrimp, the main draw is the pelagic action, with schools of trevally, barracuda, and rainbow runners often present. The nutrient-rich currents that flow along the ridge are a magnet for larger marine species. Visibility typically ranges from 20 to 30 meters, with comfortable water temperatures between 28 and 30 degrees Celsius. Diving here typically involves a drift along the ridge, often spent hovering, observing the spectacular marine life. Due to its depths and currents, this site is best suited for intermediate to advanced divers. Day trips to Koh Bon are a popular option, with some operators offering two-dive excursions. Conditions are usually good, allowing for clear views of the vibrant underwater world, making it a highlight for divers exploring the Similan National Park area.

Dive site facts: Koh Bon — West Ridge

Depth

5–40 m

Typical dive

15–22 m

Current

Mild to strong

Visibility

15–30 m

Water temperature

28–30°C

Entry

Liveaboard / day boat

Level

Intermediate–Advanced

Dive type

Wall, Slope, Reef, Drift

Night dive

Possible (liveaboards)

Region / port

Similan Islands National Park / Andaman Sea

Coordinates

8.935, 97.838

Conditions & Currents

Currents at Koh Bon West Ridge typically range from mild to moderate, though they can become strong, especially along the outer west-facing wall and around the western tip of the ridge where manta encounters are frequent. The current funnels along the ridge and can pick up suddenly, requiring divers to be prepared to hold position, particularly when observing mantas. These nutrient-rich currents, while occasionally challenging, are precisely what attract the large pelagic species to the site. Visibility is generally excellent, between 20 and 30 meters, but can temporarily reduce to 15 meters during peak manta activity due to plankton, a trade-off many experienced divers welcome. Divers should be comfortable with varied current conditions and have good buoyancy control.

Marine life & sighting chances

Manta ray

Nov-Apr (peak Dec-Mar) · common

Whale shark

Feb-Apr · occasional

Barracuda

common

Giant Trevally

common

Snapper

common

Fusilier

common

Moray eel

common

Octopus

occasional

Lionfish

common

Nudibranch

common

Leopard shark

occasional

Eagle ray

occasional

Stingray

occasional

Dive profile & how the dive runs

Dives at Koh Bon West Ridge often begin with an entry over the south-facing wall, which drops vertically. Divers then follow the reef west along the ridge. The primary objective is frequently the coral bommie that serves as a manta ray cleaning station, typically found around 15–22 meters. The dive usually progresses along the ridge, allowing for observation of both the reef life and the open blue for pelagics. The maximum depth can reach 35–40 meters at the base of the west-facing wall. Turning points are often dictated by current conditions or air consumption, with the safety stop conducted in the shallower, more sheltered bay on the east side of the ridge, or along the upper sections of the ridge itself.

Underwater photography

Koh Bon West Ridge offers exceptional opportunities for both wide-angle and macro photography. For manta rays and schooling pelagics in the blue, a wide-angle lens is essential, capturing the scale of these magnificent animals against the vibrant reef backdrop. Consider using strobes to bring out the true colors of the soft corals, which are particularly striking in pastel hues. When mantas are present, practice patience and maintain a respectful distance, allowing them to approach on their own terms. For macro enthusiasts, the healthy coral reefs host a rich variety of smaller subjects, including nudibranchs, moray eels, and diverse reef fish; a macro lens will reveal intricate details. Good buoyancy control is critical to avoid damaging the delicate soft corals and to maintain position in varying currents while composing shots.

Combine with nearby dive sites

• Richelieu Rock

  Thailand's most famous site, known for whale sharks and diverse macro life.

• Christmas Point

  Another Similan site with diverse marine life and rock formations.

• Hin Muang

  Features Thailand's largest vertical wall and frequent manta encounters.

• Hin Daeng

  Adjacent to Hin Muang, offering vibrant soft corals and pelagic sightings.

• Surin Islands — Turtle Ledge

  Offers relaxed diving with healthy reefs, suitable for all levels.

• Koh Haa — The Chimney

  A series of caverns and swim-throughs for experienced divers.

Getting there & logistics

Koh Bon West Ridge is primarily accessed via liveaboards operating from Phuket and Khao Lak. Most liveaboard itineraries that combine the Similan and Surin Islands include Koh Bon as a regular stop. Day trips by speedboat are also available, departing from Khao Lak, specifically from Nam Kem pier. These day trips typically include two dives with surface intervals for lunch and drinks. A speedboat ride from Nam Kem takes approximately one hour to reach the site. National Park fees are usually included in the day trip or liveaboard package. Trip lengths for liveaboards visiting this region generally range from 3 to 5 nights.

Safety & environment

Diving at Koh Bon West Ridge requires attention to safety due to potentially strong and unpredictable currents. Divers should maintain good buoyancy and be prepared to hold position. The nearest recompression chamber is in Phuket, meaning evacuation time could be several hours. Comprehensive dive insurance is highly recommended to cover potential medical emergencies and evacuation costs. Always dive within your certification limits and follow your dive guide's instructions, especially regarding current conditions and manta ray etiquette. Respect marine life by observing from a distance and avoid touching corals or animals to preserve the fragile ecosystem.

Who it suits — and who it doesn't

FAQ

Koh Bon — West Ridge FAQ

Liveaboards diving Koh Bon — West Ridge

These liveaboards may visit Koh Bon — West Ridge on selected itineraries — the exact dive sites depend on departure, weather and conditions.

Mandarin Queen 9

Thailand

26 guests37.5 m

Manta Queen 8

Thailand

24 guests

$127/day

The Junk

Thailand

18 guests33 m

$163/day

Deep Andaman Queen

Thailand

23 guests30.5 m

$194/day

Explorer

Thailand

16 guests25 m

$150/day

Andaman

Thailand

20 guests26 m

$108/day

Stingray

Thailand

8 guests24 m

$245/day

Seatopia

Thailand

24 guests24 m