The city of Gaya, an important pilgrim destination for performing ancestral rites is situated on the banks of the sacred river Phalgu. The name Phalgu is believed to be a combination of phala (merit) and gau (wish-fulfilling cow). The etymology implies that the river manifests the highest power of piousness and merit. The puranic literature describes the Phalgu as Mahanadi (the Great River). Among the sites of ancestral rites, the bank of the Phalgu River is given special status in mythology. Hindu pilgrims from different parts of India gather on the banks of the river during monsoon in (September – October) for the 'Pitrapaksh Tarpan ' . The pilgrims take a dip in the seasonal holy river 'Phalgu' during this season.
The river is also referred to as the ‘ Gupta Ganga' because most of the year its bed usually appears dry (if you scoop with your hand, however, you will at once come to clear water). Presently eleven ghats along the west bank of the Phalgu River are used for rituals, bathing, and ancestral rites ( Fig.3 ). The Shmashan (cremation) Ghat is the southern most and is used only for cremation rituals.
Known as the Nairanjana River in the days of the Buddha, it was along these banks that Gautama accepted a bowl of curds from the maiden Sujata and applied his re-acquired strength to the night of meditation which culminated in his enlightening.
(Source : http://www.colorado.edu/Conferences/pilgrimage/papers/Singh-3.html)