It’s still early, the last wisps of sunrise pink still hanging around in the equatorial sky, but the jungle is already busy. Swifts and swallows flutter around the sides of the Paraná do Ramos, a tributary of the world’s greatest river. A couple of toucans soar overhead, somehow simultaneously awkward and graceful in flight. “They have this large bill, almost as big as their bodies,” says Chris Bialek, an expedition guide, as he steers the big Mark 6 Zodiac carrying a dozen guests.

The heat and humidity are already building around our little boat. But, among us, the anticipation is rising even faster. We’re hoping to spot one of the world’s strangest and most sought-after animals. “These pink dolphins, they’re very rare,” says Bialek. “People come from all over the world to see them.”