Junction of a blackwater jungle stream with the silty Amazon River. Streams originating in the Amazon forests are deeply stained from the tannins of the leaf litter and referred to as "blackwater" streams. These waters can be extremely acidic, commonly with a pH of 5.0. In contrast, the Amazon river carries a heavy load of silt eroded from the Andes, and is muddy and generally neutral in pH. These muddy Amazonian rivers are referred to as "whitewater". Photo in the Peruvian Amazon, downstream from Iquitos, Peru.