The passage largely deals with ____ .

The Amazon is the largest river in the world. It carries
about a quarter of the world's running water and is the
second longest after the Nile. Much of it is brown,
brackish, piranha-infested and bitterly cold. Ranging from
narrow tributaries and raging rapids to stretches of
prodigious width and calm, the river's banks can take half
a day to reach. In parts, it can drop up to 40 metres in less
than a kilometre Furthermore, it runs through deep
canyons and steep gorges that have been carved out by
its turbulent waters.