A fast flowing stream is called a rapid. Rapids are where the water flows downhill very fast and over underwater obstacles.
Rapids
Well it is called rapids but I call it a waterfall
A fast flowing river is faster
All water and air flowing in a definite direction is called a current.
Gambusia are fish from fast flowing clean streams. Air pumps on their own do very little for them. Gambusia need filters.
rivulet Rex Drew South Africa
The measurement of how fast the current is flowing is the Ampere.
Jet streams are fast flowing, narrow air currents found in the atmospheres of some planets, including Earth.
Fast
Convection Cells
stones and fast flowing water can block the water from flowing