The Phalgu or Falgu, a river that flows past Gaya, India in the Indian state of Bihar, is a sacred river for Hindus and Buddhists. Lord Vishnu's Temple Vishnupad Mandir is situated on the bank of Phalgu river, also called Niranjana river in sanskrit and Lilagan river. Its called ଭାଲୁକୀ (Bhāluki) in Odia and is also mentioned in Odia Ramayana. Before attaining Enlightenment, the prince Siddhārtha Gautama practiced asceticism for six years (ten or twelve years according to some accounts) on the banks of the river, residing in a forest near the village of Uruvilvā. After realizing that strict asceticism would not lead to Enlightenment, he recuperated after bathing in the river and receiving a bowl of milk-rice from the milkmaid Sujātā.

He sat under the nearby pippala tree, where he finally achieved Enlightenment. This tree became known as the Bodhi Tree, and the site became known as Bodh Gayā.

The Phalgu is formed by the confluence, some 3 kilometres (2 mi) below Bodh Gaya, of the Lilajan (also called Niranjan or Nilanjan) and the Mohana, two large hill streams each of which is over 270 metres (300 yd) wide. The Phalgu is also mentioned as Niranjan. The united stream flows on to the north past the town of Gaya, where it attains a breadth of over 820 metres (900 yd). The Phalgu here passes by a high rocky bank, on the steep sides of which are many paved stairs leading down to the river bed, while high above are the Vishnupad Mandir, with many minor shrines around it. It then runs in a north-easterly direction for about 27 kilometres (17 mi), and opposite the Barabar hills it again takes the name of Mohana, and divides into two branches which eventually flow into a branch of the Punpun.

The Phalgu like its confluent streams, Lilajan and Mohana, is subject to high floods during the monsoons but in other seasons of the year it dwindles to a stream wandering through a wide expanse of sand.

Before attaining Enlightenment, the Siddhārtha Gautama practiced asceticism on a tributary of the river.

There is reference to the city of Gaya and the Phalgu in the Ramayana in which it says that Sita had cursed the Phalgu River. There is an interesting story and the purana states that on account of this curse, the Phalgu lost its water, and the river is simply a vast stretch of sand dunes. According to mythology, in the absence of Rama, his wife Sita offered pinda on its banks to Dasharatha father of Rama.

The story goes that Rama, along with his brothers and Sita, came to Gaya to perform the sacred rites for his father, Dasaratha. When the brothers were bathing in the river, Sita was sitting on the banks, playing with the sand. Suddenly, Dasaratha appeared out of the sand, and asked for the Pindam, saying he was hungry. Sita asked him to wait till his sons returned, so that she could give him the traditional Pindam of rice and til. He refused to wait, asking her to give him pindams made of the sand in his hand.

Having no other option, in the presence of five witnesses – the Akshaya Vatam, the Falguni River, a cow, a Tulsi plant and a Brahmin, she gave him the Pindam he desired. Soon, Rama returned and started the rituals. In those days apparently, the ancestors would arrive in person to collect their share, and when Dasaratha did not appear, they wondered why. Sita then told them what had happened, but Rama could not believe that his father would accept pindams made of sand. Sita now mentioned her witnesses, and asked them to tell Rama the truth.