The area through which the main river and all its tributaries and distributaries flow is called the river basin. Thus the basin provides water to the river which is obtained from rain, melting snow etc. and is channelized through the various rivers and their branches into the main river which again break up to form distributaries that drain into the sea.
Among all the rivers basins in India, the Ganga River Basin is the biggest. It has an area of nearly 8.38 lakhs sq. km.
It is followed by the Godavari River Basin with an area of nearly 3.23 lakhs sq. km.
The 3rd largest basin is that of the Brahmaputra followed by the Indus. Both have nearly 2.85 lakhs sq. km. in area within India, individually.
The 5th largest basin in Krishna with 2.7 lakhs sq. km. Mahanadi Basin with 1.9 lakhs sq. km. is sixth followed by Narmada Basin 94.5 thousand sq. km. and Kaveri Basin 94.4 thousand sq. km.