Nobres

The rivers around Nobres and the district of Bom Jardim run out of limestone, and the calcium carbonate they carry precipitates and settles the sediment, which leaves the water clear enough to see thirty or forty metres. The standard activity is flutuacao: a wetsuit, mask and snorkel, and a slow drift downstream with the current, watching dourado, piraputanga and pacu move past in numbers. Rio Triste and the Aquario Encantado are the usual sites. The same limestone produced the Lagoa das Araras, where red-and-green macaws come to the palms morning and evening, and the Gruta da Lagoa Azul, a cave with a blue lake that lights up when sun enters through the roof at the right hour of the day.

What you actually see

• Flutuacao downriver - drifting in a mask through very clear spring water.
• Shoals of river fish - dourado, piraputanga and pacu at close range.
• Lagoa das Araras - macaws coming to the palms at either end of the day.
• Gruta da Lagoa Azul - a cave lake lit blue when the sun angle is right.

When to go

May to September, the dry season, when water is clearest. Two days.

Honest expectations

Every site is privately run with its own fee and daily cap, and booking ahead is necessary in season. Costs add up quickly. Rain upstream clouds the water for days. The blue cave only shows its colour within a narrow window of hours.

Nearby

Cuiaba is south-east; Chapada dos Guimaraes is east.