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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.
tributary
tributary
tributary
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
Ocean current
currents
current people
A river?
A river?
An ocean current.