A tributary is that river which joins the main river and increases the volume of water. It is generally found in the upper or the middle course of a river, eg. Yamuna is the main tributary of Ganga.
A distributary is that river which originates from a main river. It is formed near the river’* mouth before it falls into the sea. It is found in the lower course of the river. Eg. Hooghly is the main distributary of the Ganga.
