Koh Bon West Ridge
Depth is the range from the top of the site to its usual maximum; "recommended cert" is the mainstream-agency level operators usually ask for, not a legal rule. Currents and visibility change daily — treat everything here as planning ranges.
Koh Bon's western ridge is Thailand's most reliable manta station. The limestone spur steps down from the island to a nose at around 18-25 m where cleaning stations operate, and reef mantas arrive on their own schedule to bank in slow circles overhead, sometimes one, sometimes a squadron that stays the whole dive. Etiquette is drilled: hold the reef side, stay low, let the animals run the geometry. Manta-less days still pay in yellow soft coral on the ridge's north face, octopus in the rubble, and napoleon wrasse cruising the steps. Liveaboards revisit until the mantas oblige.
The moment you come for: Reef mantas at cleaning stations, a diveable ridge line in all currents, repeat-visit rhythm
Topography: Limestone ridge stepping down to a deep point
Current: The ridge nose catches flow from both sides; mantas prefer it that way.
Know before you splash
Hazards: Current at the nose and depth creep following mantas off the ridge.
Conservation: Cleaning stations fail when divers crowd them; the low-and-still protocol is enforced by every good crew.
Nitrox: Worth it here — profiles sit in the range where enriched air meaningfully extends no-stop time (with the training to use it).
Who you'll meet
Common Reef (Day) Octopus
Napoleon (Humphead) Wrasse
Nudibranchs
Oceanic Manta Ray
Reef Manta Ray
For photographers
Wide angle: ★★★★★ · Macro: ★★☆☆☆ — editors' 1–5 rating of what this site gives each style of shooting