The Rig-Veda authors mention their land as that of seven rivers. Out of the seven only five exist now. The remaining two, Saraswati and Drishadwati have disappeared. Following the discovery of Mohenjo-Daro along the banks of Indus and Harappa about 350 miles away, archaeologists started looking for other sites in the area. New sites were discovered, but they were buried under the sand in the desert. Archaeologists knew that these towns could not survive in the desert and satellite images have now shown that in what is now Thar Desert, once traversed a river with its own fertile banks. These dry channels of the Ghaggar-Hakra is considered by many to be the Saraswati river.
A recent paper by Fuller and Madella describe the importance of Ghaggar-Hakra system in Indus-Saraswati Civilization
Another factor in the Holocene environmental history of the northwestern sub-continent, overlooked in some discussions of Quaternary palaeoecology, is the changes in the river drainage system, especially the Ghaggar-Hakra system flowing roughly parallel but separate to the Indus . Archaeological research in Cholistan has led to the discovery of a large number of sites along the dry channels of the Ghaggar-Hakra river (often identified with the lost Sarasvati and Drishadvatirivers of Sanskrit traditions) . Along the Ghaggar-Hakra there is a relatively high frequency of settlements during the Mature Harappan (2600–2000 cal BC), which suggests a well-watered region that could support agriculture. This may be interpreted either as a river or an inland delta in the area around Derawar. By the time of the Painted Grey Ware period (ca 1200–500 cal BC) the river must have been dry, because several sites of this period are found in river bed contexts. This change, thought to have been brought on by tectonic uplift and the capture of the Ghaggar-Hakra headwaters by the Yamuna watershed, led to gradual desiccation during the Holocene, which was well underway by the period of the Harappan Civilisation The final desiccation of some of these channels may have had major repercussions for the Harappan Civilisation and is considered a major factor in the de-centralisation and de-urbanisation of the Late Harappan period. [via email from Carlos Aramayo]