Up the Rio Negro
The dark river that flows into Manaus from the remote reaches of northwestern Amazonas is known as the Rio Negro. Its somber hue is actually more dark reddish-brown than black, yet it is known as a “black” river due to the fact that its waters are filled with rotting vegetation from low-lying forests. The abundance of decaying organic matter results in a high level of acidity.
As a result, its waters don’t have the same fertilizing properties as “white” rivers such as the Solimões. A bonus is that the high acidity kills insect larvae, which results in a low instance of mosquito attacks.
© Michael Sommers from Moon Brazil, 2nd Edition