Tributary is the answer you are looking for, I believe.
A stream or river called that flows into a larger stream or river is called a tributary.
The middle part of a river may be called mid-stream, mid-river or mature river.
A large natural stream, which may be a waterway.
A small stream in a river is called a current.
No, a stream is actually smaller than a river.
Are you crazy? A stream or a small river is called a TRIBUTARY.
A tributary.
A Tributary
The difference between a river and a stream is the name applied to it by local residents, and relative size. In the same region, something called a river is usually larger than something called a stream. However, something that is called a river in one place could be the same size as something called a stream in another place.
river
I was told it was an "exotic stream."
A tributary of a river is a tributary.It might be a stream, a creek, or another river that empties into the first river.