a meander
meander
Water is called a stream when flowing in a definite direction.
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.
Upstream or up river
Upstream or up river
When a contour line crosses a river or stream, they make a "V" shape and points to the direction the river is flowing.
Are you crazy? A stream or a small river is called a TRIBUTARY.
A tributary.
Bay of Fundy