The headwaters of the Ganga is called Bhagirathi and it is fed by the Gangotri Glacier joined by the Alaknanda at Devprayag in Uttarakhand. At Haridwar, the Ganga emerges from the mountains on to the plains. The Ganga is joined by the various rivers like Yamuna, Ghaghara, Gandak and Kosi. The river Yamuna rises in the Yamunotri glacier in the Himalayas. It flows parallel to the Ganga and as a right bank tributary meets the Ganga at Allahabad. The Ghaghara, the Gandak and the Kosi rise in the Nepal Himalaya. They are the rivers, which flood parts of the northern plains every year, causing widespread damage to life and property, whereas, they enrich the soil for agricultural use. The main tributaries, which come from the peninsular uplands, are the Chambal, the Betwa and the Son. These rise from semi-arid areas, have shorter courses and do not carry much water in them.

Ganga Basin _{Image Courtesy: Wikipedia}

The Ganga river system is explained in this video.

Some of the learners also asked:
Which delta is formed by the River Ganga?