Āpagā (Apaga) is a river; and there is a pilgrimage site named after this river. In Mahābhārata (Mahabharata) it is said that the river is located about one krośa (krosa, about two miles) away towards the east of Mānuṣatīrtha (Manushatirtha, the pilgrimage site called Manusha). It is hailed as a site of great virtue. It is also a suitable site for performing the funeral rites of the deceased parents.

In Padmapurāṇa (Padmapurana), too, the location of this river is describes as it is in Mahābhārata —
āpagā (apagā) mānuṣasya tīrthasya krośamātre mahīpate
apagā nāma vikhyātā nadī siddhaniṣevitā.

Another name of the river Āpagā (Apaga) is Āpayā (Apaya). Probably this change is due to the vernacular usage.
In Ṛgveda (Rigveda)it is said that Āpagā flows across the land which is between the rivers Sarasvatī (Saraswati) and Dṛṣadvatī(Drishadwati). Since it is said that the ancient land of Kurukṣetra (Kurukshetra) is located in between Sarasvatī and Dṛṣadvatī. So Āpagā is also supposed to be flowing across Kurukṣetra.
In Karṇaparva (Karnaparva)of Mahābhārata, there is a mention of another river called Āpagā. This river flows across the city of Śākala (Sakala), the capital of Madra.
śākalaṁ nāma nagaraṁ āpagā nāma nimnagā.

According to Cunningham, Āpagā is another name of the river Āyuka (Ayuka) or Āyaka (Ayaka) flown across the west of the river Rābhī (Rabhi).
The river Āpagā had been dried up long ago. Later a channel was made up in its lost way, and that channel was named Āpagayā (Apagaya).