Before we begin to describe what a river is, let us remember that water is now turning into a luxury. It is thus become an obligation for humans to keep their water sources clean. A river is a natural watercourse, usually freshwater, flowing toward an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. A small river is also known as stream, creek, brook, rivulet, tributary or a rill. There are number of rivers in the world but most of them these days are polluted. But still in this world of pollution and contamination, there are few rivers which are completely clean. So here is a list of five cleanest rivers in the world. Have a look!