The side of a stream is usually called its bank.
Douglas Hodkiewicz
It's called "bank." As in river bank.
The sides are known as the river bank or river banks.
A stream or river called that flows into a larger stream or river is called a tributary.
Meanders are created in the stream bed when a shallow graded stream cuts from side to side in its erosion process.It will create cliffs on the outside of the bends, and smooth banks on the inside of the stream. These features will migrate upstream.
The word that can precede "stream" and "side" is "river."
because there is a highi side and a low side up stream dwn stream
It is occasionally called a sinking stream or a disappearing stream, but geographers and geologists normally call it a stream, just like another stream.
A small stream is called a creek.
Tributary is the answer you are looking for, I believe.
a tributary
a waterway is a large stream
a stream