Quote Originally Posted by furiousuk View Post
Thanks Akerbeltz, just the sort of thing I was after! I'd thought I'd seen something like this in a map of Eastern Africa (although I might be thinking of Lake Victoria which is further inland) but maybe I didn't. I've just zoomed in to have a look at Istanbul, just so I've got this right, the Black Sea exits through Istanbul to the Sea of Marmara and from there out to the Aegean and then the Med? And just so my geographical knowledge is sound: there can be no other exits from the Black Sea? Just the same as a lake?
Right, it flows through the Bosphorus into Marmara and then through the Dardenelles into the Aegean. There straits act very much like rivers at first glance, the surface current flows from the Black Sea to the Med, but then there's an undercurrent which flows the opposite way. Tidal shifts can cause very quick changes in the currents, which has always made the straits treacherous to pass through.

If you want your sea to function like the Black Sea then it must have only one exit point as far as I understand it. With multiple exits or a larger exit it would be more of an estuary, which would also be a very fine explanation.