Also Me Getting To Deep With Geological And Rock Formations Of The Ionian Sea To See If Springs Or Rivers Could Have Been Plausible - Tumblr Posts

Don´t worry it would have been worse if you went the Odysseus the bioenginner route™, that would have been craizier, also I don´t think there´s a geological map of Ithaca, (we don´t have a clue where it is)

btw it's fantasy, you really don't need to worry about your world map making "sense" geologically or whatever. make that river flow backwards from the sea into the mountain.