The park exists because of a signature on Decision 91/2001/QĐ-TTg, dated 8 June 2001, by which Vietnam's prime minister upgraded the Northern Phú Quốc Islands Preservation Zone into a national park. The protected area runs to 31,422 hectares — officially reckoned as roughly seventy percent of the island — and is split three ways: 8,603 hectares under strict protection, 22,603 hectares designated for biological restoration, and 33 hectares for administration and services. That last figure is worth pausing on. A third of a square kilometre of offices and gates governs an area a thousand times its size. The boundary swallows the communes of Gành Dầu, Bãi Thơm and Cửa Cạn entirely and takes bites out of Cửa Dương, Hàm Ninh, Dương Tơ and Dương Đông township, which means almost every settlement on Phú Quốc shares a fence line with it.

Phú Quốc tilts. The high ground gathers in the north and the northeast, where Núi Chúa reaches 603 metres and the ridges below it are drained by streams that run hard in the monsoon and vanish in the dry months. The Rạch Cửa Cạn carries most of that water westward to the sea. Forest holds the slopes: dipterocarp species in the uplands, and in the low, wet ground the peculiar pale-barked melaleuca, which tolerates flooding that would kill anything else. Botanists have recorded 929 plant species on the island as a whole and more than 470 within the park itself. The difference between those two numbers is the story of the rest of the island — the part that was cleared, planted, and, more recently, paved.

The mammal list reads like an inventory of things that are hard to see. Silvered langurs travel the canopy in troops. Slow lorises and pygmy lorises move at night at a pace that makes them almost invisible by daylight. Crab-eating macaques and stump-tailed macaques work the forest edges, small-clawed otters hunt the streams, and fruit bats cross the island at dusk in numbers that make the sky look briefly wrong. Underwater the accounting is more precise: 125 fish species, 132 molluscs, 62 kinds of seaweed. Two marked trails let visitors in on foot, including a five-kilometre route near Gành Dầu on the northwestern corner, where the road east runs through forest dense enough that the sea disappears entirely for several kilometres.

In 2006 UNESCO folded the park into something far larger. The Kiên Giang Biosphere Reserve spans 1,188,106 hectares, of which 858,801 are ocean — a designation that treats the coral, the seagrass and the mangrove as one continuous system with the forest, because ecologically they are. Eighty-nine species of hard coral grow within it. Hawksbill and green turtles forage the seagrass beds, and so does the dugong. The tension in all of this is not hidden: Kiên Giang's fisheries production ranks highest of any province in Vietnam, and the same shallow water that feeds the boats is the pasture the dugong cannot do without. Phú Quốc's northern hills are protected. What happens in the two metres of water off their beaches is a harder question, and it is being answered now.