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  The upper phase of the river Ganges begins at the confluence of the Bhagirathi and Alaknanda rivers in the town of Devprayag in the Garhwal division of the Indian state of Uttarakhand. The Bhagirathi is considered to be the source in Hindu culture and mythology, although the Alaknanda is longer, and therefore, hydrologically the source stream. The headwaters of the Alakananda are formed by snow melt from peaks such as Nanda Devi, Trisul, and Kamet. The Bhagirathi rises at the foot of Gangotri Glacier, at Gomukh, at an elevation of 4,356 m (14,291 ft) and was mythologically referred to as residing in the matted locks of Shiva; symbolically Tapovan, which is a meadow of ethereal beauty at the feet of Mount Shivling, just 5 km (3.1 mi) away.
  
  Although many small streams comprise the headwaters of the Ganges, the six longest and their five confluences are considered sacred. The six headstreams are the Alaknanda, Dhauliganga, Nandakini, Pindar, Mandakini and Bhagirathi. Their confluences, known as the Panch Prayag, are all along the Alaknanda. They are, in downstream order, Vishnuprayag, where the Dhauliganga joins the Alaknanda; Nandprayag, where the Nandakini joins; Karnaprayag, where the Pindar joins; Rudraprayag, where the Mandakini joins; and finally, Devprayag, where the Bhagirathi joins the Alaknanda to form the Ganges.
  
  After flowing for 256.90 km (159.63 mi) through its narrow Himalayan valley, the Ganges emerges from the mountains at Rishikesh, then debouches onto the Gangetic Plain at the pilgrimage town of Haridwar. At Haridwar, a headworks diverts some of its water into the Ganges Canal, which irrigates the Doab region of Uttar Pradesh, whereas the river, whose course has been roughly southwest until this point, now begins to flow southeast through the plains of northern India.
  
  The Ganges river follows a 900 km (560 mi) arching course passing through the cities of Bijnor, Kannauj, Farukhabad, and Kanpur. Along the way it is joined by the Ramganga, which contributes an average annual flow of about 495 m /s (17,500 cu ft/s) to the river. The Ganges joins the 1,444 km (897 mi) long River Yamuna at the Triveni Sangam at Prayagraj (previously Allahabad), a confluence considered holy in Hinduism. At their confluence the Yamuna is larger than the Ganges contributing about 58.5% of the combined flow, with an average flow of 2,948 m /s (104,100 cu ft/s).
  
  Now flowing east, the river meets the 400 km (250 mi) long Tamsa River (also called Tons), which flows north from the Kaimur Range and contributes an average flow of about 187 m /s (6,600 cu ft/s). After the Tamsa, the 625 km (388 mi) long Gomti River joins, flowing south from the Himalayas. The Gomti contributes an average annual flow of about 234 m /s (8,300 cu ft/s). Then the 1,156 km (718 mi) long Ghaghara River (Karnali River), also flowing south from the Himalayas of Tibet through Nepal joins. The Ghaghara (Karnali), with its average annual flow of about 2,991 m /s (105,600 cu ft/s), is the largest tributary of the Ganges by discharge. After the Ghaghara confluence, the Ganges is joined from the south by the 784 km (487 mi) long Son River, which contributes about 1,008 m /s (35,600 cu ft/s). The 814 km (506 mi) long Gandaki River, then the 729 km (453 mi) long Kosi River, join from the north flowing from Nepal, contributing about 1,654 m /s (58,400 cu ft/s) and 2,166 m /s (76,500 cu ft/s), respectively. The Kosi is the third largest tributary of the Ganges by discharge, after Ghaghara (Karnali) and Yamuna. The Kosi merges into the Ganges near Kursela in Bihar.
  
  Along the way between Prayagraj and Malda, West Bengal, the Ganges river passes the towns of Chunar, Mirzapur, Varanasi, Ghazipur, Ara, Patna, Chapra, Hajipur, Mokama, Begusarai, Munger, Sahibganj, Rajmahal, Bhagalpur, Ballia, Buxar, Simaria, Sultanganj, and Farakka. At Bhagalpur, the river begins to flow south-southeast and at Farakka, it begins its attrition with the branching away of its first distributary, the 408 km (254 mi) long Bhāgirathi-Hooghly, which goes on to become the Hooghly River. Just before the border with Bangladesh the Farakka Barrage controls the flow of Ganges, diverting some of the water into a feeder canal linked to the Hooghly for the purpose of keeping it relatively silt-free. The Hooghly River is formed by the confluence of the Bhagirathi River and Ajay River at Katwa, and Hooghly has a number of tributaries of its own. The largest is the Damodar River, which is 625 km (388 mi) long, with a drainage basin of 25,820 km (9,970 sq mi). The Hooghly River empties into the Bay of Bengal near Sagar Island. Between Malda and the Bay of Bengal, the Hooghly river passes the towns and cities of Murshidabad, Nabadwip, Kolkata and Howrah.
  
  After entering Bangladesh, the main branch of the Ganges river is known as the Padma. The Padma is joined by the Jamuna River, the largest distributary of the Brahmaputra. Further downstream, the Padma joins the Meghna River, the converged flow of Surma-Meghna River System taking on the Meghna's name as it enters the Meghna Estuary, which empties into the Bay of Bengal. Here it forms the 1,430 by 3,000 km (890 by 1,860 mi) Bengal Fan, the world's largest submarine fan, which alone accounts for 10–20% of the global burial of organic carbon.
  
  The Ganges Delta, formed mainly by the large, sediment-laden flows of the Ganges and Brahmaputra rivers, is the world's largest delta, at about 64,000 km (25,000 sq mi). It stretches 400 km (250 mi) along the Bay of Bengal.
  
  Only the Amazon and Congo rivers have a greater average discharge than the combined flow of the Ganges, the Brahmaputra, and the Surma-Meghna river system. In full flood only the Amazon is larger.