Parts of A River

The bed of a river is the surface upon which it flows. Its banks are the sides that hold it in bounds. Right bank and left bank are terms frequently misunderstood. The right bank is on the right of an observer looking downstream (in the direction in which the river flows), the left bank on the observer's left.

A river begins at its source or headwater usually in a lake, spring, glacier, snowfield, swamp, or marsh—and flows to its mouth. A mouth is the point at which a river enters and ends in a larger body of water. The Mississippi, for example, has its source in Minnesota's Lake Itasca and its mouth in the Gulf of Mexico.

The course of a river is its path, which follows line of lowest elevation between the source and the end of the stream. Courses are often divided into three sections: the upper course, or that nearest the source; the middle course; and the lower course, that nearest the mouth. The channel, depending on how the word is used, is either the river's bed or the line of deepest water throughout the river's course.