This is what shastras/Purana's say about the Jamuna river-
"In Mandarachal, A mango fell from a mango tree into a river changing the river's colour to yellow. Because of this, the river was called "Arun". On the downside of the river there was a Syzygium cumini tree where one syzygium cumini fell and changed the colour of the river to black, again changing the name of the river to Jambu river (Also known as Jamuna)"
"Because a Syzygium cumini fell on Jambunada, it was known as Aruna."
This proves that Jambunada and Aruna river are the same.
In "Padmapurana", Swargakhanda, Chapter 38, Shlok 65:
This intersection is in Nepal close to "Varahachetra" (eastern Nepal) where Jamuna river intersects with Kausiki. If this is the case, then how is it possible that Jamuna is in india? Which one is the real Jamuna? the one that the shastras/Puranas say or the one that is in Northern India?
Note: I do not wish to offend anyone regarding my question. Our current thirthas are as holy regardless of their authenticity and I respect their location. Being a Hindu, I would never disrespect any thirth just because they do not match with shastras. Many thirthas have changed locations and this is why I try to find their original location. Sorry if I have offended anybody.