How does river differ from sea?

A river flows from an underground source, usually from a spring under a mountain and into an ocean or a sea. A sea is a moderately sized body of water. Most seas are usually bigger than Lake Superior.
A sea is salty because it is apart of an ocean. A river is fresh water.

A river always leads to a sea, the opening of the river is called the mouth. All rivers separate into many streams like roots. This is the other side of the mouth.