Are all the rivers alike?
Different regions in Amazonia can be quite distinct, with their own water color, clarity and bottom substrate. Some rivers have hard sand bottoms, others are rock filled, while others are clay bottomed. Fish, insect, bird and mammal species can vary greatly from river to river. Soil type and topography dictate what type of vegetation grows near the river. Some rivers have cypress-like flowering trees growing right in the water along the bank. Others are palm lined, while still others boast towering deciduous trees reaching hundreds of feet above the river.
For more detailed information see: A Peacock Bass Primer - Part II - 'The Fishery' - a section about Amazonian rivers.