Vagina.
A stream or river called that flows into a larger stream or river is called a tributary.
Tributary is the answer you are looking for, I believe.
A small stream in a river is called a current.
The middle part of a river may be called mid-stream, mid-river or mature river.
Are you crazy? A stream or a small river is called a TRIBUTARY.
A tributary.
River
A stream?
A stream.
It is called a tributary.
I was told it was an "exotic stream."
A fast-moving stream is called a river or a torrent.