An increasingly popular argument amongst Out-of-India-Theory (OIT) advocates (Koenraad Elst for example) is that is that the Indo-Aryan etymologies of rivers in the Rig Veda disprove an Aryan migration into India. They claim that native river names would have survived post-migration.
Some of the proffered etymologies for Vedic rivers are rather flimsy, but no matter. There is a much more fundamental issue with this line of argument: the evidence shows that migrants often do not adopt indigenous river names. In fact, Indo-European migrants to Western Europe used names with clear Indo-European etymology for most major rivers.
If OIT advocates believe that Indo-Aryan etymologies for rivers in North India prove the Indo-European languages originated in India, then they must explain why nearly all the major rivers of Europe have such solid Indo-European etymologies:
Thames: Old English Temes, from PIE *tm̥Hes, cognate with Sanskrit támas
Loire: Gaulish *liga, from PIE *legʰ
Seine: Latin Sequana, from PIE *seykʷ, cognate with Sanskrit siñcáti
Rhine: Gaulish Rēnos, from PIE *h₃reyH, cognate with Sanskrit riṇā́ti
Po: Latin Padus, from PIE *bʰudʰmḗn, cognate with Sanskrit budhná
Elbe: Old German *albī, from PIE *h₂elbʰós, cognate with Sanskrit ṛbhú
Danube: Celtic *Dānowyos, from PIE *déh₂nu, cognate with Sanskrit dā́nu
Dnieper: Sarmatian *dānu *apara, from PIE *déh₂nu + *h₂epero, cognate with Sanskrit dā́nu + ápara
Dniester: Sarmatian *dānu *nazdya, from PIE *déh₂nu + *nésdyos, cognate with Sanskrit dā́nu + nédīyas
Don: Sarmatian *dānu, from PIE *déh₂nu, cognate with Sanskrit dā́nu
Vistula: Latin Vistula, from PIE *weys