An ocean current.
A current. A rotating current is called a gyre.
Its not Oceans
A stream or river called that flows into a larger stream or river is called a tributary.
a tributary
what is wáter at flows in streams and river into the ocean sand lakes
The stream of water which flows like a river through the ocean is a current. The Gulf Stream is the most significant such current which flows from the tropics to the northern latitudes.
it is called a tributary
tributary
Gulf Stream
It could be called runoff, feeder stream or source.
A tributary.
There is no single name for a single stream of water that flows into an ocean but headwaters would be a good one for a single stream of water into a lake