They
are doing almost everything in the water!
People live next to the rivers because their whole lives depend on the water. They travel on the water. They drink the water. They bathe and wash clothes in the water. They fish for food in the water. When it got really hot in the middle of the day, some people I saw even walked into the water to cool off while they were visiting - with their clothes on!
This water is very dark. The river is called Rio Negro, or "Black River". When it joins another lighter main tributary, and becomes the Amazon River, the waters mix their colours in pretty swirls.
The water is so dark that you can't see the fish, which are just under the surface. I guess the piranhas are in a different area of this river!