"Blackwater rivers" are "jungle tea"

Many rivers are dark enough to be called “blackwaters” and for some, it even gets into the name. One of the largest tributaries of the Amazon, and the fifth greatest river in the world by discharge, is called the Rio Negro because of the organic matter that darkens its waters. Yet even among these, the Ruki stands out.

Like other blackwater rivers, the Ruki gets its color from dissolved organic compounds (DOCs) in its waters. Ironic as it may seem, its lack of sediment also contributes. Although soil darkens a clear mountain stream, it’s seldom as black as the tropical forest matter that gives the Ruki its color. The Ruki runs through nearly flat territory, so it doesn’t scrape up much sediment.

On the other hand, the heavy rains in the area wash DOCs from plant material on the forest floor. During the rainy season, the same flatness causes large areas to flood, and remain underwater for weeks, leaching even more compounds out. “The Ruki is essentially jungle tea,” Drake said.

More information at IFL Science.