They are called tributaries.
They join together; Many small streams becomes on big one and the big ones lead to the river
With other streams or tributaries joining, a stream's flow of water increases until it can be considered a river. For example, the mighty Mississippi starts out as a trickle of water near the Canadian border. Many similar trickles begin to join it and the flow increases.
in the wet part of the river
The tributaries of a river are the streams or smaller rivers that join the main river. for example, the Missouri River is the chief tributary of the Mississippi.
All streams in Kansas eventually lead to the Mississippi River
Part of the longest river in the world, call the river Nile.
The part of a river that empties into a body of water is called the mouth of the river
That is the mouth of the river.
Usually it is the upper reaches (often termed as mountain streams) that flow the fastest. In the lower, flatter valleys, rivers tend to slow down (except in spate, when the river is in flood)).
It's called either the river mouth or the river delta.
The Nile River delta.
a rainbow