Mud! Moms hate it, kids love it. Whatever your feelings about the stuff, mud itself is crucial to the forest ecosystem. Mud is the result of ground-down rock, eroded stone and soil that all end up in the river. Mud is the ultimate source of nutrients in the Amazon soil. When the river floods, millions of tons of mud are deposited along the river banks, changing the river course and renewing soils. This annual enrichment allows permanent agriculture along the banks of the river that is impossible in most other areas of the forest that are not so lucky. So actually it's a good thing to be a "stick in the mud!"
As the river washes the edges of recently deposited mud, it collapses and breaks away, leaving shelves and ledges that are eventually washed away by the inexorable current. The color of the mud depends on the parent material and according to its origin may be any color from pale gray to black.
As the sources of water high in the mountains decline and as rainfall drops, the waters of rivers throughout Amazonia recede. In places, where rivers are very shallowsuch as here on the upper Napo in eastern Ecuadorvast plains of mud are left behind. These places are virtually impassable and offer endless breeding grounds for swarms of sandflies.