Ganga Dussehra is celebrated on the tenth day of Shukla Paksh in the month of Jyeshtha, as the day when Goddess Ganga, incarnated on the Earth. Goddess Ganga is the personified form of the river Ganga.
As per Skanda Purana, the day is very auspicious for taking a bath in the holy river. This day is also considered for meditation and charity. Not only this, it is also believed that the ten sins of a person are destroyed if he takes a bath in a holy river on this day.
A person gets rid of all his sins if he chants the Ganga Stotra while standing amidst the waters of the river. On this day, the devotee should offer ten things to the deity, and donate ten things to charity. This leads to the clearance of ten of his sins. Among all the ten sins, three are relating to the body, three to the speech and three relating to mind. Hence, it is a good opportunity for those who have some guilt or past regrets, troubling them inside.
Maharaja Sagar once decided to organise a yagna. His grandson, Anshuman declared that he would protect the horse to be used during the Yagna. Lord Indra, however, stole the horse. This was something very inauspicious for the yagna.
Enraged by this, the grandson of Sagar, Anshuman, headed on to search for it along with his army of sixty thousand men. When they could not find the horse on the Earth, it was decided that the horse must be looked for in the Patal Loka. There they found the horse standing near Maharishi Kapil, who had been meditating, unaware about the horse's presence.
However, the men started shouting 'thief, thief' at Maharishi Kapil. When Maharishi, opened his eyes, burning with anger, the whole army of sixty thousand turned into ashes.
Bhagirath was the son of Maharishi Dileep. He sat in deep mediation for the liberation of the souls of these men. He worshiped Lord Brahma through meditation and when Brahma appeared before him and asked for his wish, he requested for the incarnation of Goddess Ganga on the Earth.
However, Brahma knew how difficult it would be for the Earth to tolerate the velocity of the river Ganga. He therefore, asked Bhagirath to seek the permission of Shiva who is the only one who can handle the river.
Upon Bhagiratha's request, Lord Shiva agreed to let the river Ganga pass through the strands of his matted hair, so that, the velocity gets balanced. The river was now a peaceful, beautiful, and divine river, the water of which is considered nectar and is used for all holy rituals.
One must take bath in a holy river on this day. Mantras in the praise of Goddess Ganga must be chanted while taking the bath. While worshiping the deity, all the items kept for offering must be ten in numbers. Ten kinds of flowers, ten fruits and so on. Barley and sesame seeds must be given to charity, for which an amount equivalent to sixteen fists can be taken.
Ganga Dussehra is celebrated with huge religious fervor in almost all the parts of India. Fairs are organised around water bodies. River Yamuna is also worshiped on this day. The kite flying events are organized in many parts of the country.
A holy bath, which is one of the most pious rituals for the Hindus, becomes even more significant on this day. However, people also take a bath in other nearby water bodies, or minor rivers, if not possible in the Ganga river. Chanting the mantras of her name itself makes the bath, a sacred one.