The source
it forms at the beginning of a stream or river
Answer!-Usually the start of a river is called its source and the end of the river is called the mouth.
The source of a river is where it starts as a tiny stream. The other end is the mouth, where it reaches the sea.
A stream or river called that flows into a larger stream or river is called a tributary.
The stream is a tributary of the river.
A stream or brook can get bigger and become a river.
A small stream in a river is called a current.
Ohio River
From the beginning... Pakuranga Stream starts at a storm drain on Casuarina Road. It then runs along Aviemore Drive. Soon it joins up with another stream calling it a tributary. Then it runs under Cascades Road and joins it with another stream making it officially a big stream known as a river. Then it runs under Ti Rikau Drive. Eventually the river joins with another river and soon enough it leads to Half Moon Bay.
The middle part of a river may be called mid-stream, mid-river or mature river.
No, a stream is actually smaller than a river.
Tributary is the answer you are looking for, I believe.