" A river flowed through Eden and watered the garden. From there the river branched out to become four rivers. The first river, named Pishon, flows around the whole land of Havilah, where there is gold. The gold of that land is excellent. Bdellium and onyx are also found there. The second river, named Gihon, flows around the whole land of Cush. The third river, named Tigris, flows out of Assyria towards the east. The fourth river is the Euphrates."
I have a theory, yet another one, that these rivers are in fact the oceans, and as such they flow around the continents rather than nations within a continent. As there was once just one supercontinent I suppose they could have started as Rivers but grown to Oceans once the continents separated. It makes sense as there are four rivers and four lands, and we now have four continents. Or at least it makes sense in my head, what d'you think?