The Ribeirão das Águas Quentes is routinely described as the only river in the Americas with hot-water rapids, and whatever the fine print on that claim, the experience is genuinely strange: current, noise, tumbling water over stones, and none of the cold that your body expects to come with them. The volume is the other surprise. The springs push out 6,228,000 litres every hour — more than 149 million litres a day — which is enough that the resort pools downstream are completely replaced with fresh spring water on a continuous basis rather than filtered and recycled. Nothing here is heated. Nothing is pumped from a boiler. The plumbing is a kilometre of rock, and the only machinery involved is gravity. An entire resort district has been built on that fact, and on nothing more elaborate than water that shows up warm and keeps showing up.

The springs were recorded in 1722 by the bandeirante Bartolomeu Bueno da Silva — the son, following the trail of his more notorious father — and named Caldas Velhas, the old hot springs. The bandeirantes were hunting gold and enslaved people across the interior, not health resorts, and the find sat largely unexploited for two centuries afterward. What eventually changed things was not the water but the road. Once Goiânia and Brasília existed and could be reached in an afternoon's drive, a naturally heated river 178 kilometres from one and 360 from the other stopped being a curiosity and became an asset.

Rio Quente only became a municipality in 1989, splitting from neighbouring Caldas Novas, and it is small by any measure: 256.7 square kilometres, with 3,864 urban residents (2022) and 486 rural residents (2007). Its economy is almost purely tourism. Rio Quente Resorts runs seven hotels here, the Hotel Pousada being the first ever built, and they draw visitors in numbers that dwarf the resident population year-round. There is some farming — rice, corn, sugarcane, dairy cattle — but it is a rounding error beside the hotels. The arrangement has worked out unusually well for the people who live here: Rio Quente's human development index in 2000 was 0.806, seventh of the 242 municipalities in Goiás, with adult literacy at 93.3 percent against a national average of 86.4. There is no hospital in town. Caldas Novas, 28 kilometres east, has one.

None of this works without the high ground. Part of the 12,315-hectare Caldas Novas State Park falls inside the municipality, and what it protects is not a view but a mechanism: the plateau is the main recharge zone for the geothermal aquifers that feed both Rio Quente and Caldas Novas, together the largest hydrothermal complex in Brazil. Rain that lands up there is the rain that comes back up warm down here, and it lands mostly between November and March, in a climate that averages 23 degrees at the surface. Pave the plateau, or strip its soils, and the springs eventually notice. It is a rare case where the conservation argument needs no poetry at all — the watershed is the business.