The Amazon Basin is a vast waterway system. No two rivers are the same, but rivers are generally classified into three major buckets due to their color. Let’s look at these classifications and what causes the color variations. 

BLACK WATER RIVERS:

Black Water and beautiful beaches make up the Rio Negro, the largest Black water river.

The most visited type of river by anglers due to it being the home of the largest species of peacock bass the Cichla, Temensis. Blackwater rivers are often described as a tea coloration.

A common question is what causes the tea coloration? To answer this question please see the explanation from the book The Amazon: What Everyone Needs to Know.

Blackwater rivers represent a freshwater tea created when plant matter that has fallen or washed into the river fails to completely decompose. The sandy soils surrounding blackwater rivers support few microorganisms that would otherwise decompose the leaf litter remnants, and the high concentrations of tannins and other plant compounds remain suspended in these rivers, giving them their characteristics color and making them highly acidic. (1)

Another valuable explanation comes from the book. Floods of Fortune: Ecology & Economy Along the Amazon.

Blackwater rivers, which are free of heavy sediment but dark in color. They owe their special character to the millions of years of erosion that have ground down the Brazilian and Guiana highlands into sands that now fill the Amazon Basin. Because millions of years of weathering, the sandy soils are very poor in nutrients. The streams that are born on them are among the most chemically pure on Earth. Why, then, the blackness?

It turns out that the sandy soils are too poor in microorganisms (especially fungi, bacteria, and invertebrates) to easily decompose organic matter. Organic chemicals, moreover, that would easily bind to clay sediments have no affinity for sand. The organic overload thus seeps through the soil and is carried into streams and rivers, rendering some as dark as tea. Blackwater rivers are highly acidic, with a pH usually below 4.0. (2)

To clarify, this doesn’t mean that Blackwater rivers are low in aquatic life. Peacock bass must have a stable and abundant food source to grow to the size that they do.

The lower Rio Negro harbors the most diverse fish fauna of any freshwater river in the world, having twice as many species (700) as all the rivers of western Europe combined. Most of these species are relatively small in size.” (1)

BLUE (OR CLEAR) WATER RIVERS:

Wolfish below a small rapid in a Clearwater Amazon River.

Blue water rivers are often clear and beautiful.

Rivers and streams that drain uplands to the east of the Andes are usually clear or almost so. These waterways arise in the old, worn-away mountains of the Brazilian Highlands to the south and the Guiana Highlands to the north. Chemically these clear water rivers range from acidic to nearly alkaline, but in general they are relatively nutrient-poor. The three largest clearwater rivers are the Rio Tapajos, Rio Xingu, and Rio Tocantins. All drain the Brazilian Highlands and enter the Amazon River from the south. (2)

Just as Rocky Mountain streams are effected by annual snow melt runoff, peak times during the rainy season can make these clear water streams temporarily off colored. For that reason, we generally do not fish during peak flows.

At the multi-species destination, the Rio Aripuanã, the river is clear and anglers can often spot fish while floating down the river. This makes for visual and exciting sport fishing opportunities.

WHITE WATER RIVERS

Rio Madeira

These White Water Rivers are not referring to rivers for paddle sports. These rivers have a high sediment load and are often a milky, coffee color. The Rio Solimoes which by many is considered the beginning of the Amazon River is a White Water River.

Amazonian whitewater rivers-despite the name-are more of a café-au-lait muddy brown than white. The color is due to sediments derived from the Andes.

These muddy rivers begin as clearwater streams in the Eastern Andes, where they start their descent into the Amazonian lowlands, gathering sediment along the way. As such, in the words of Michael Goulding, “the Andes are the main nutrient bank for the Amazon.” And the main body of the mighty Amazon-called the Rio Solimoes in Brazil-is a whitewater river. (1)

If you would like to see a map of the Amazon Basin distinguishing the major rivers by their river type, then please see the link below and scroll to the 4th page:

READ MORE HERE

Resources:

1.  The Amazon: What Everyone Needs to Know. Mark J. Plotkin. Page 38,39.

2. Flood of Fortune. Ecology & Economy Along The Amazon. Michael Guilding, Nigel J.H. Smith, and Dennis J. Mahar. Page 5, 6,7

3.  A Classification of Major Naturally-Occuring Amazonian Lowland Wetlands. Multiple Authors. See page 3 for map.