The streams that contribute to a river system are called tributaries.
waters of the ocean that move in giant streams are called currents.
Streams of molten lava out of a volcano are called 'lava flows'.
They are called naiads.
jet streams
creeks
Jet streams~ Rebecca
Solar Flares or giant streams of gas
It is usually the other way round. Moving in the direction of water flow, streams merge together to form larger rivers, the streams are called the river's tributaries. The point of joining is called a "confluence".
a glacial deposit that is sorted and layered by streams or melted water is called
tributaries
These are often called currents, but sometimes are just called streams e.g. The Gulf Stream