Drishadvati is a tributary of holy Saraswati River. It is mentioned in the Rig Veda, the most ancient text. The Nadistuti in Rig Veda makes a specific mention of this river along with Sindhu with its five tributaries in the east, and Saraswati, Ganga, Yamuna and Sarayu.
Several scholars identify Saraswati as the present day Surasti in Punjab, which is a small river. Sursati falls into the present day Ghaggar, another small river which is also said to be the lost Saraswati River. Likewise, Drishadvati is identified as the present day Chitang or Rakshin Punjab, anther rivulet. It appears that in ancient times the present day Sursati-Ghaggar-Haka-Nara must have formed a considerable stream as Saraswati. The present day Chitang is a tributary of Ghaggar.
Drishadvati was a big river in those days. Saraswati was also a substantially large river. Even Puranas include these in the list of major rivers. Later accounts, however, say that Saraswati had vanished in the desert at Vinasana near Sirsa in Haryana and reappeared at Plaksha Prasravana at the sea.
During the time of Rig Veda, Kashi and Ganga had not acquired the pride of place among the holy river. The two rivers – Saraswati and Drishadvati – were the holiest, the regions covered by them being the holy Brahmavarta.