Koh Bon West Ridge

Khao Lak · Phang Nga · Thailand

Koh Bon is already famous in the Similan National Park circuit for its manta ray encounters, but most divers experience only the sheltered southern bay. The West Ridge is the island's wilder face, a granite formation extending from the western headland into the open Andaman Sea, exposed to the full force of oceanic currents and the deep water that begins just a few hundred metres offshore. This is big-animal diving on the Similan's exposed frontier. The ridge is composed of massive granite boulders stacked and tumbled by geological forces, creating a three-dimensional structure of overhangs, swim-throughs, and vertical faces from five metres to beyond forty. The current hits the ridge hard from the west, sweeping nutrients along the rock face and creating upwellings that concentrate plankton against the granite. This nutrient concentration is the key to everything that lives here. Manta rays use cleaning stations on the ridge year-round, but the encounters here differ from the gentler bay. Mantas arrive into the current, approaching the cleaning boulders at speed before settling into a hover above the rock while cleaner wrasses work their gills and skin. The current makes positioning challenging; divers must find shelter behind boulders and wait rather than swimming to intercept. I held position behind a granite outcrop at twenty metres, current ripping past my fins, and watched three mantas work the cleaning station in rotation. A fourth appeared from the blue, a large female with at least a four-metre wingspan, and the others shifted position to accommodate her. Below, leopard sharks rested on the sandy patches between boulders, their spotted bodies camouflaged against the substrate. The West Ridge's exposure to open ocean means that anything can appear from the blue. Whale sharks pass during plankton season. Schools of yellowfin tuna blur through at speed. Giant trevally hunt in packs along the ridge edge. The unpredictability is part of the appeal: each dive on the West Ridge carries the anticipation of an encounter that the sheltered bay simply cannot deliver.