Ganga is a river of northern India and Bangladesh. The river has a long history of reverence in India and is worshipped by Hindus as a goddess. It often called the 'holy Ganga'.

The total length of the river is about 2,510 km (1,557 mi). Along with another river Yamuna, it forms a large and fertile basin, known as the Gangetic plains, stretching across north India and Bangladesh, and supports one of the highest densities of human population in the world. Indeed, about one in every 12 people on earth (8.5% of world population) live in its catchments area. Due to this incredible concentration of population, pollution and the destruction of habitats is a matter of serious concern.
 

The Ganga is definitely mentioned in the Rig-Ved, the earliest and the holiest of the Hindu scriptures. The Ganga is mentioned in the nadistuti (Rig Veda 10.75), which lists the rivers from east to west. In RV 6.45.31, the word Ganga is also mentioned, but it is not clear if the reference is to the river.

RV 3.58.6 says that "your ancient home, your auspicious friendship, O Heroes, your wealth is on the banks of the Jahnavi (JahnAvyAm)". This verse could possibly refer to the Ganga.[1] In RV 1.116.18-19, the Jahnavi and the Gangetic dolphin occur in two adjacent verses. [2] [3]

During the early Indo-Aryan Ages, the Indus and the Saraswati were the major rivers, not the Ganga. But the later three Vedas seem to give much more importance to the Ganga, as shown by its numerous references.

Hindus also believe life is incomplete without bathing in the Ganga at least once in their lifetime.

According to the Hindu Purans, Goddess Ganga used to exist only in Heaven. Then prince Bhagirath worshipped Ganga to descend on earth. This is why Ganga is also known as Bhagirathi. In the Mahabharath also this story is mentioned. In fact Ganga is a major character in the Mahabharath where she's the mother of Bhisma.
 

Varanasi is closely associated with Ganges. The temple town has many temples along the banks of the Ganges. In Hinduism, the river Ganga (feminine) is sacred. It is worshipped by Hindus and personified as a goddess, who holds an important place in the Hindu religion. Hindu belief holds that bathing in the river on certain occasions causes the forgiveness of sins and helps attain salvation. Many people believe that this will come from bathing in Ganga at any time. People travel from distant places to immerse the ashes of their kin in the waters of the Ganga; this immersion also is believed to send the ashes to heaven. Several places sacred to Hindus lie along the banks of the river Ganga, including Haridwar and Kashi. People carry from Ganges, sacred water that is sealed in copper pots after making the pilgrimage to Kashi. It is believed that drinking water from the Ganga with one's last breath will take the soul to heaven.

In most Hindu families, a vial of water from the Ganga is kept in every house. This is done because it is auspicious to have water of the Holy Ganga in the house, and also if someone is dying, that person will be able to drink its water.

Many Hindus believe that the water from the Ganga can cleanse a person's soul of all past sins, and that it can also cure the ill. The ancient scriptures mention that the water of Ganges carries the blessings of the Lord's feet. Hence mother Ganges is also known as Visnupadi [Emanating from the Lotus feet of Supreme Lord Sri Visnu].

Some of the most important Hindu festivals and religious congregations are celebrated on the banks of the river Ganga such as the Kumbh mela or the Kumbh fair and the chhat puja.

The largest religious gathering on Earth for Hindu peoples. Around 70 million Hindus from around the world participated in Kumbh Mela at one of the Hindu Holy city Prayaga (also known as Allahabad) (India). The most important city sacred to Hinduism on the banks of the river Ganga is Varanasi or Banaras. It has hundreds of temples along the banks of the Ganga which often get flooded during the rains. This city, especially along the banks of the Ganga, is an important place of worship for the Hindus as well as a cremation ground.
 

The Gangotri Glacier in the Uttaranchal Himalayas is the origin of the Bhagirathi river, which joins the Alaknanda river at Devaprayag, also in the Uttaranchal Himalayas, to form the Ganga. The river then flows through the Himalayan valleys and emerges into the north Indian plain at the town of Haridwar. This section sees extensive Whitewater rafting and kayaking from September to March.

Ganges river delta, Bangladesh and India, the Ganga then flows across the broad plains of north India, (called the Gangetic Plains), and forms the major river basin of that vast region. Its tributaries include the Kosi, the Gomti, the Sone, and above all the Yamuna. The Yamuna River — a major river in its own right, and nearly as endowed with the sanctity of Religious tradition and legend as the Ganga, is in fact a tributary of the Ganga; their confluence marks the site of the pilgrim town of Prayag, now known as Allahabad. Not only sites of religious significance, but also many of the most populous industrial cities of northern India lie on the banks of the Ganga, including Kanpur, Allahabad, Varanasi and Patna.

Early morning on the Ganges at the city of Varanasi, swollen by the waters of a wide basin that draws from watersheds as diverse as the Himalayas and the Aravallis, the Ganga forms a formidable current in the stretch between Allahabad and Malda, and thereafter, a large delta. Near the town of Malda in West Bengal, it undergoes its first attrition with the branching away of the Hoogly, its first distributary. The city of Kolkata (previously Calcutta) stands on the banks of the Hoogly. The main stream of the river (known as the Padma River) then enters Bangladesh. Here, it unites with the Jamuna branch of the even larger Brahmaputra river. The combined stream then joins with the Meghna River before flowing out to sea. In the flat plains of Bangladesh, the Ganges splits almost immediately into a dense network of distributaries, all of which finally empty into the Bay of Bengal.

The region encompassing the delta near the Bay of Bengal coast is known as The Sundarbans (Beautiful Forests) — a region of thick mangrove forests, and one of the major habitats of the Royal Bengal Tiger. Two species of dolphin can be found in the Ganges, the Ganges River Dolphin and the Irrawaddy Dolphin. The Ganges is also notable in that it contains a rare species of freshwater shark, Glyphis genetics, about which little is known.