Rivers, such as the Sapta Sindhu ("seven rivers"), play a prominent part in the hymns of the Rigveda, and consequently in early Vedic religion. It may have been derived from an older Proto-Indo-Iranian hydronym, as a cognate name, hapta həndu, exists in the Avestan language.
A recurring theme in the yajur veda is that of Indra slaying Vritra (literally "the obstacle"), liberating the rivers; in a variant of the myth, Indra smashes the Vala cave, releasing the cows that were within. The two myths are separate however, rivers and cows are often poetically correlated in the Rigveda, for example in 3.33, a notable hymn describing the crossing of two swollen rivers by the chariots and wagons of the Bharata tribe,
- 3.33.1cd Like two bright mother cows who lick their youngling, Vipas and Sutudri speed down their waters. (trans. Griffith) 
The Sapta Sindhu are a group of seven chief rivers of uncertain or fluctuating identification (the number seven is of greater importance than the exact members of the group, compare the Saptarishi, and also the (later) seven seas and the seven climes) of the Avesta. The Avesta's hapta həndu are preemptively equated with the Vedic Sapta Sindhavaḥ or vis-a-vis: in Vendidad 1.18 these are described to be the fifteenth of the sixteen lands created by Mazda.
Identity of the seven rivers
It is not entirely clear how the seven rivers were intended to be enumerated. They are often located in the in northern India / eastern Pakistan. If the Sarasvati and the five major rivers of the Punjab are included (Sutudri, Parusni, Asikni, Vitasta, Vipas (Vipāś), the latter all tributaries of Sindhu/Indus), one river is missing, probably the Kubha. (The Sindhu is a special case, having feminine or masculine gender). Other possibilities include the Arjikiya or Sushoma; compare also the list of ten rivers, both east and west of the Indus, in the Nadistuti sukta, RV 10.75. In 6.61.10, Sarasvati is called "she with seven sisters" (saptasvasā) indicating a group of eight rivers, the number seven being more important than the individual members (see also saptarshi, hapta karšuuar /haft keshvar in Avestan), so that the list of the Sapta Sindhu may not have been fixed or immutable. In RV 10.64.8 and RV 10.75.1, three groups of seven rivers are referred to (tríḥ saptá sasrâ nadíyaḥ "thrice seven wandering rivers"), as well as 99 rivers. The Sapta-Sindhu region was bounded by Saraswati in the east, by the Sindhu in the west and the five in between were Satudru, Vipasa, Asikni, Parusni and Vitasta.
Not all researchers agree with this interpretation. In his book "Land of the Seven Rivers", writer Sanjeev Sanyal has argued that the Sapta Sindhu refers only to the Sarasvati and its own tributaries. If Sanyal is right, the Sapta Sindhu region only refers to a small area including Haryana and a part of north Rajasthan but leaving out most of Punjab. According to his interpretation, Sapta Sindhu is only a small subset of the Rig Vedic terrain and its disproportionate importance derives from it being the original homeland of the victorious Bharata Trutsu tribe.
Geography of the Rigveda
Identification of Rigvedic rivers is the single most important way of establishing the geography of the early Vedic civilization. Rivers with certain identifications stretch from eastern Afghanistan to the western Gangetic plain, clustering in the Punjab (Five waters(rivers)). Some river names appear to go back to common Indo-Iranian rivers, with cognate river names in Avestan, notably the Sarasvati (Avestan Haraxvaiti, Old Persian Hara(h)uvati) and the Sarayu (Iran. Harayu, Avestan acc. Harōiiūm, mod. Persian Harē).
A number of names can be shown to have been re-applied to other rivers as the center of Vedic culture moved eastward from the central Vedic heartland in the Punjab. It is possible to establish a clear picture for the latest phase of the Rigveda, thanks to the Nadistuti sukta (10.75), which contains a geographically ordered list of rivers. The most prominent river of the Rigveda is the Sarasvati, next to the Indus. The Sarasvati river of the Rigveda is commonly identified with the present-day Ghaggar-Hakra, although the Helmand River as a possible locus of early Rigvedic references has been discussed. This is mostly ascribed to the movement of Vedic Aryans from their early seats in Seistan (Arachosia, Avestan Haraēuua), Gandhara and eastern Afghanistan into the Indus plains and beyond. Which is the widely a linguistic point of view ascribing to Aryan migration without substantial archaeological evidences. On the other hand archaeologists like B.B. Lal have shown the possibility of reverse westward movements of some Indo-aryan clans from indus basin as well as the absence of the certain archaeological trace for any outside intrusion to the subcontinent.
In the geographical organization of the following list, it has to be kept in mind that some names appearing both in early and in late hymns may have been re-applied to new rivers during the composition of the Rigveda.
Northwestern Rivers (western tributaries of the Indus):
- Trstama (Gilgit)?
- Anitabha (listed once, in 5.53.9, with the Afghan rivers Rasa (Avestan Rangha/Raŋhā), Kubha, Krumu, Sarayu (Avest. Harōiiu)
- Rasa (on the upper Indus (often a mythical river, Avestan Rangha, Scythian Rha)
- Kubha (Kabul), Greek Kophēn
- Krumu (Kurrum)
- Mehatnu (along with the Gomati and Krumu)
- Suvastu (Swat) in RV 8.19.37)
- Gauri (Panjkora)??
- Kusava (Kunar)??
The Indus and its minor eastern tributaries:
Central Rivers (rivers of the Punjab):
East-central Rivers (rivers of Haryana):
- Sarasvati (References to the Sarasvati river in the Rigveda are identified with the present-day Ghaggar River, although the Arghandāb River (a tributary of Helmand River) as a possible locus of early Rigvedic references has been discussed.)
- Drsadvati, Apaya (RV 3.23.4, Mahabharata Apaga.)
Uncertain / other
- e.g. RV 2.12; RV 4.28; RV 8.24
- H.-P. Schmidt, Brhaspathi and Indra, Wiesbaden 1968
- Gnoli 1989 pp.44–46
- S.C. Sharma. 1974. The description of the rivers in the Rig Veda. The Geographical Observer, 10: 79-85.
- Michael Witzel, Tracing the Vedic dialects in Dialectes dans les litteratures Indo-Aryennes ed. Caillat, Paris, 1989, 97–265.
- Gherardo Gnoli, De Zoroastre à Mani. Quatre leçons au Collège de France (Travaux de l’Institut d’Études Iraniennes de l’Université de la Sorbonne Nouvelle 11), Paris (1985)
- Shrikant G. Talageri, The Rigveda, a historical analysis, Aditya Prakashan, New Delhi (chapter 4)