During Meenakshi Thirukalyanam, Ganga is supposed to have flown out Lord Sundareshwarar's locks (Lord Shiva) to quench Gundotharan's thirst. And this stream came to be known as Vaigai. Meenakshi Thirukalyanam episode is dated 3138 BCE as per the article at https://www.booksfact.com/history/meenakshi-thirukalyanam-madurai-20-february-3138-bce.html. This means Vaigai is about 5000years old
But there is the story of Matsya Avatara where King Satyavrata, in the Chakshusha manvantara, used to meditate on the banks of river Kritamala. It is said that this Kritamala river is now known as Vaigai.
This is really confusing. Can someone clarify please