A thousand miles inland, this river is eight miles wide. Get in and you can feel it pull you along toward the coast. You get on a boat at the dock in Manaus; the river here is the Rio Negro—the clear-tea Black River. Enter the river, go under water, turn your face to the sun, and look up and it is like seeing the sun through dark tea, which is pretty much what the river is. All the vegetation of the trees along the river falls into the stream and steeps in the near-equatorial waters. Though dark, the water is very clear and unclouded.

But go 20 miles downstream and the Rio Negro spills into the clouded waters of the Amazon. Because the waters of the black river are different from the temperature of the Amazon, the two waters do not mix for a long time. There is a line—as clearly as if drawn by a hand—that marks where the waters of the Rio Negro end and those of the Amazon begin and this line continues downstream in the Amazon for many miles until they finally dissolve into each other.

And wild. You can travel for hours on the river without seeing any signs of civilization whatsoever. Not a house or a boat or even a plane overhead. There isn’t even a sign of near-civilization. This river is one of the darkest places I have ever been in my life with a sky that contains more stars than it seems possible for a sky to hold. But strange stars, unfamiliar to my north-hemisphere eyes. The Southern Cross is the only one I come to recognize and I lie on the boat canopy at night and look for it. Somehow, my night is unfulfilled and unsatisfying until I have seen it.