Ganga

There is a story which describes how the river Kaveri (also spelled Cauvery) arrived on earth by sage Agastya. Once due to hot whether in south his wife Lopamudra fainted. There were no rains and people suffered intensely. The lands became parched and cracks appeared. Animals and birds could not get food or water, their suffering was beyond words. All over the land there was sheer misery lack of food and water made life unbearable. Agastya felt sad and approached lord Shiva for help. Shiva gave him small amount of Ganga in his Kamandala (small pot which he was carrying) and said wherever you spill this water the river will flow from there.

Since a demon named Surapaduman (Later killed by Lord Murugan) wanted to destroy the south with no water and food, planned to take the kamandala from Agastya,

Lord Ganesha took a form of crow and disturbed Agastya, perched on the Kamadala and thrown the kamandala on earth. Ganesh drifting water from Kamandala After touching earth, the water drifted out of kamandala and took a form a river Kaveri

http://en.wikipedia.org/wiki/Kaveri
http://www.cauvery.com/