<P> The hydrology of the Ganges River is very complicated, especially in the Ganges Delta region . One result is different ways to determine the river's length, its discharge, and the size of its drainage basin . </P> <P> The name Ganges is used for the river between the confluence of the Bhagirathi and Alaknanda rivers, in the Himalayas, and the India - Bangladesh border, near the Farakka Barrage and the first bifurcation of the river . The length of the Ganges is frequently said to be slightly over 2,500 km (1,600 mi) long, about 2,505 km (1,557 mi), to 2,525 km (1,569 mi), or perhaps 2,550 km (1,580 mi). In these cases the river's source is usually assumed to be the source of the Bhagirathi River, Gangotri Glacier at Gomukh, and its mouth being the mouth of the Meghna River on the Bay of Bengal . Sometimes the source of the Ganges is considered to be at Haridwar, where its Himalayan headwater streams debouch onto the Gangetic Plain . </P> <P> In some cases, the length of the Ganges is given for its Hooghly River distributary, which is longer than its main outlet via the Meghna River, resulting in a total length of about 2,620 km (1,630 mi), from the source of the Bhagirathi, or 2,135 km (1,327 mi), from Haridwar to the Hooghly's mouth . In other cases the length is said to be about 2,240 km (1,390 mi), from the source of the Bhagirathi to the Bangladesh border, where its name changes to Padma . </P> <P> For similar reasons, sources differ over the size of the river's drainage basin . The basin covers parts of four countries, India, Nepal, China, and Bangladesh; eleven Indian states, Himachal Pradesh, Uttarakhand, Uttar Pradesh, Madhya Pradesh, Chhattisgarh, Bihar, Jharkhand, Punjab, Haryana, Rajasthan, West Bengal, and the Union Territory of Delhi . The Ganges basin, including the delta but not the Brahmaputra or Meghna basins, is about 1,080,000 km (420,000 sq mi), of which 861,000 km (332,000 sq mi) are in India (about 80%), 140,000 km (54,000 sq mi) in Nepal (13%), 46,000 km (18,000 sq mi) in Bangladesh (4%), and 33,000 km (13,000 sq mi) in China (3%). Sometimes the Ganges and Brahmaputra--Meghna drainage basins are combined for a total of about 1,600,000 km (620,000 sq mi), or 1,621,000 km (626,000 sq mi). The combined Ganges - Brahmaputra - Meghna basin (abbreviated GBM or GMB) drainage basin is spread across Bangladesh, Bhutan, India, Nepal, and China . </P>

Where does most of the water that flows through the ganges river come from