(i) When any elevated area, such as a mountain or an upland, separates two drainage basins, such an upland is known as a water divide. For example; Ambala is located like a water divide between Indus and Ganga Basin.

(ii) The largest river basin in India is the Ganga river basin which is spread over 8,61,404 sq. km. area.

(iii) The Indus river originates near Tibbet, Near Mansarovar Lake and the Ganga river originates from the Gangotri Glacier and is joined by the Alaknanda at Devprayag in Uttarakhand.

(iv) The two headstreams of the Ganga are Bhagirathi and Alaknanda. They both meet at Devprayag to form the Ganga.

(v) The Brahmaputra in its Tibetan part has less silt, despite a longer course because, in Tibet, it carries smaller amount of water as it is a dry and cold area. While in India, it carries a large volume of water and silt because it passes through a region of high rainfall.

(vi) Tapi and Narmada are the two peninsular rivers which flow through a trough.

(vii) Lakes:

• Lakes help to regulate the flow of rivers.
• During heavy rainfall it prevents flooding and during the dry season, it maintains an even flow of water.
• Lakes can also be used for developing hydel power.
• They help in moderating the climate of the surroundings, maintain the aquatic ecosystem, and increase the natural beauty.

Rivers:

• Rivers' water is a basic natural resource which is essential for various human activities.
• riverbanks have attracted settlers from ancient times. These settlements have now turned into big cities.
• Using river water for irrigation, navigation, and hydro-power generation is of great significance.