Scientists generally refer to smaller bodies of flowing water as streams and larger ones as rivers. The area of land from which rainfall and melted snow drain into a particular stream or river is called its watershed or catchment. The high ground separating watershed is called a divide. Every place on earth is part of some watershed.
Every watershed reflects the land it drains.
The quality of water within a watershed and the species of fishes that can be found within its boundaries are directly linked to the quality of the land and any use it is put to by humans. As streams join other streams, a branching network, or river system, forms. Stream ordering is a way of indicating in numerical terms the relative position of a stream within a much larger river system. Headwater streams that have no tributaries or branches are called first order streams. They usually begin from cool springs arising in a hillside or wetland, or as an outlet from a lake or pond.