Whitewater rivers are characterized by very muddy waters, resembling coffee with milk. This is caused by the large quantities of sediments they carry.
Whitewater rivers arise mostly in the Andes and are characterized by high turbidity and high nutrient content. Because of the large number of tributaries in the Andes the Amazon River is considered a whitewater river. Map: Wildlife Conservation Society, 2016.
In the Amazon Basin, major tributaries with headwaters in the Andes, in the upper basin, are turbid and classified as whitewater. However, it is important to clarify that the small tributaries in the headwaters of the Andes that are above 400 m elevation are also considered whitewater, even though their waters may run relatively clear during parts of the year when rainfall is low, owing to intact slopes, vegetation cover, and favorable water chemistry.
On the geological scale, the Andes are a very young mountain chain and the materials that compose them are poorly compacted, which makes them sensitive to erosion. Thus, eroded material is easily mobilized and transported downstream all the way to the Atlantic Ocean.
Locally, these rivers are often referred to as whitewater rivers, though the term should not be confused with the English term «whitewater,» which refers to turbulent rapids and is commonly used by kayakers.
Andean whitewater tributaries include the Madeira, Ucayali, Marañón, Putumayo-Içá and Caquetá-Japurá rivers. There are also several tributaries that do not have headwaters in the Andes but are considered whitewater rivers because of their relatively high sediment loads, such as the Purus and Juruá.
Given the large amount of sediment they carry, whitewater rivers have a higher nutrient content than blackwater and clearwater rivers, with calcium being the predominant ion in the water. The pH of whitewater rivers is often near or above neutral (7.0). At elevations higher than approximately 2,000 m in the Andes, the pH of river water can be above 8.0.