The river that is not in existence at present is the Saraswati river.

What is Saraswati river?
Saraswati river is one of the major rivers of ancient India, which finds mention in the Rigveda. It is considered to be a sacred river by Hindus and is associated with the goddess Saraswati, who is the goddess of knowledge, music, and arts.

Why it is not in existence at present?
The river Saraswati was once a mighty river that flowed through northern India. However, over time, due to various geological changes and human intervention, the river dried up and is not in existence at present. It is believed that the river dried up around 4000 years ago, during the Indus Valley Civilization.

Factors responsible for the disappearance of Saraswati river:
1. Geological changes: The Saraswati river originated in the Himalayas and flowed through the north-western region of India. However, due to geological changes, the river's course was altered, and it started to lose its volume.

2. Deforestation: Deforestation in the region also played a significant role in the drying up of the river. The cutting of trees resulted in soil erosion and the loss of natural water storage capacity, leading to the decline in the flow of the river.

3. Human intervention: The construction of dams, canals, and other water diversion projects also contributed to the drying up of the river. The water from the river was diverted for irrigation and other purposes, resulting in a decline in the water flow.

In conclusion, the Saraswati river was a significant river in ancient India, but it is not in existence at present due to various factors such as geological changes, deforestation, and human intervention.