tribuetrees
Its is called a tributary
Tributary.
a little bed of water flows and the joins a bigger bed of water, where it joins a stream and then another stream to a bigger stream, then a river which joins a bigger river then goes down to a waterfall where it joins a lake.
A Tributary.
A stream or river called that flows into a larger stream or river is called a tributary.
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.
confluence
The 'Water of Leith' is the principal stream, and North East Valley Stream joins that at the Gardens. There is also the Kaikorai Stream as well.
It starts at a storm drain on Casuarina Road then runs along side Bucklands Beach road to 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.
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.