Established in 1981, Phang Nga National Park lies in the sheltered waters north and east of Phuket Island. Its pale, milky-green water is the setting for more than 80 spectacular islands, often rising to 300 metres and more. People have sailed the waters of Phang Nga for at least 3000 years. The islands of Phang Nga are part of a geological feature which extends all the way from south of Krabi north to the southern provinces of China. Technically, Phang Nga is referred to as a drowned karstland.

At one time this was a barrier reef thousands of kilometres long. From the onset of the Permian Age, roughly 230 million years ago, corals and other marine organisms laid down deposits of calcium carbonate hundreds of metres thick. Then, movements in the earth's crust came to exert enormous pressures on this sedimentary rock. Rather than bend and fold, the inelastic limestone ruptured. Blocks of stone sheered away one from the other, some thrusting up while others sank.

Other forces have played their role in sculpting the dramatic cliffs and natural monuments: periodically, the earth's icecaps have expanded and retreated, alternately taking up and releasing massive quantities of sea water, raising and lowering sea levels worldwide by more than 150 metres. The most recent occasion was 8500 to 10000 years ago, when the icecaps last retreated. Before that, this had all been dry land, and these islands mountains. As the ice melted, the sea rose dramatically, pouring into the valleys and low-lying areas between the mountains of Phang Nga. Wind, waves and currents taking up the job of carving which had been largely left of since the previous inundation.

These days, the waters of the bay average only a few metres. The bottom is silt which has been deposited by several rivers which flow into the bay from the north. That also explains the milky-green colour of the water. Deciduous limestone scrub forest crowns most of the islands and the mainland. Taller, evergreen forest can be found in the valleys, where the soil is deeper and richer.

Plants such as pandanus, elegant cycads, euphorbs and prickly pear cactus establish themselves even on the sheer cliff faces, sending their roots into the tiniest crack and subsisting on rainwater or merely on the humidity. Mangrove swamps are in evidence between the islands and around estuaries, but most of them are coastal mangroves and found outside the park boundary. Those inside are largely degraded and illegal exploitation continues. The 1989 logging ban in Thailand excluded mangrove forests, many of which are outside protected zones and parcelled out to concessionaires.