In Hindu religion, anything can become pious. God pervades everything ranging from the mammoth stars to the tiniest atoms. All the innate things are the forms of the God. God is everywhere, omnipresent. Therefore even stones can become the objects of veneration. So are many kinds of trees, rivers, hills and mountains are revered in Hinduism. Many of them have some form of association with the Gods. For example, the rat is the vehicle of Lord Ganesha. Siva mounts the bull Nandi which can be seen in the stone casts squatting outside the temples of Siva. There is a mammoth statue of Nandi bull in the Chamundi Hills of Mysore. The pedestrian journey to the temple atop the hill begins from here.
Rivers are considered sacred. This is logical also because they provide us with the water which sustains the life by helping grow the crops, drinking, bathing and transporting. In fact many great cities and civilizations flourished on the banks of the great rivers. The most prominent example is the Indus valley civilization which existed on the rivers in Punjab. Thus many rivers are held in most esteem by the Hindus.
Ganga is one such river. It is thought to have sprang from the foot of Vishnu, flowed over the sky in the form of milky way(Mandakini) and descended to earth with great force. The terrific effect of its impact was smothered by Siva who absorbed its great strength in his matted locks. Like her tributary Yamuna it is revered as a Goddess. Other river like this is imaginary river Saraswati which was supposed to flow underground and meet the Ganga and Yamuna at the Prayag sangam which is a most holy place for Hindus. Mughal emperor Akbar was so impressed by the great Kumbh fair there that he named the city as Allahabad. Other rivers held in esteem are Krishna (also called Kistna), Godavari and Cauvery. Certain lakes, notably Manasa in the high Himalayas near mount Kailash and lake Puskara near Ajmer in Rajasthan are held divine.