Vlad Tepes - buna ziua ! but no, city was on the lake shore not the sea coast. I've had several (bigger) lakes, on various maps, on the shores of which the AI built functional harbours and far-less useful ships. I just mentioned an extreme case. Since ships can enter and leave cities from and to any adjacent water tiles, in the case of Athens (above) there would actually be access to the harbour by ships passing through the city.
I do have to add that I am not certain as to whether the above is always true, or if the location of the Harbour has to be on the shore of a body of salt water. This I cannot test in my current game, and I have cleared out my old ones.