Explosive craters tend toward roundness, but few hold the line as neatly as this one. The shoreline of Yeak Laom closes an almost perfect circle around a surface of about 0.44 square kilometres, and the walls drop steeply enough that the lake reaches fifty metres in the middle without much shelving at the edge. Nothing significant flows in and nothing flows out, which is why the water is so startlingly clear — a deep green in the middle of the day, going nearly black under the forest shadow at the rim. There are no volcanoes erupting in Cambodia now. Ratanakiri's basalt plateau is the cooled residue of a much older restlessness, and the lake is the most legible piece of evidence left.

The forest around the rim survives because the lake is not treated as scenery. Yeak Laom and the woods that enclose it hold spiritual significance for the Tampuan, who make ritual offerings here at planting and at harvest, and when someone in a family falls ill. The Tampuan number around 31,000 and are the largest of Ratanakiri's indigenous peoples, speaking a Mon–Khmer language of the Bahnaric group — unrelated, despite the shared uplands, to the Austronesian Jarai a short distance east. Tampuan society is matrilineal and animist, organised around villages of a few hundred people, and known well beyond the province for its gong music. The lake belongs to that world first. Everything else built around it has had to fit.

By the early 1990s the pressure was showing: litter accumulating, farmland pushing at the rim. In 1995 the provincial authority and the International Development Research Centre began conservation and environmental education work alongside the Tampuan communities living around the crater, and in 1997 the communities themselves took the project over. That handover mattered. Cambodian law did not recognise indigenous community land rights until 2001, so the arrangement ran ahead of the legal framework rather than behind it. Day-to-day decisions sit with a community-based tourism committee of ten elders, one man and one woman drawn from each of five Tampuan villages, and the money taken at the gate goes back into the villages and into protecting the lake. In 2018 a sub-decree formally established the Boeng Yeak Laom Multiple Use Area, covering 36.2 hectares.

It is a ten-minute run from Banlung by car or tuktuk, and the entrance fee is deliberately tiered — a quarter of a dollar for Cambodians, two dollars for foreign visitors. A three-kilometre footpath circles the whole lake beneath the canopy, and wooden platforms let you drop straight into water warm enough to stay in for hours; life jackets are handed out at the edge. A small museum near the entrance sets out Tampuan culture in the villagers' own framing rather than a visitor's. Handicraft stalls sell what the surrounding villages make, along with fresh honeycomb, rice wine, dried beef and wild fruit. Come in the dry stretch from December to February for the clearest water and the easiest walking; July is the wettest month of the year, and the path turns to red mud.