A river usually has 3 main courses,   the upper course, the middle course  and the lower course.

 

 Usually a river has 3 main courses, so the first course ,which is the upper course, starts from the mountain top 'till the part where it reaches the ground. Then there is the middle course which starts from the ground to the middle of the river ,and last but not least there is the lower course which starts from the middle of the river till it empties out to the sea or ocean.