Vilayet Salinity?

This is just a minor detail for one of my campaigns, but I’m the sort who likes to get setting details right. As I believe the Vilayet Sea is what will one day become the Caspian Sea, I am inferring that, like the Caspian, the Vilayet is a saltwater sea. This may or may not be confirmed in REH’s stories or in the game sourcebooks, but I’m not sure. Can anyone confirm the freshness or salinity of the Sea of Vilayet? Thank you!