Two watchers on two sides of a creek
They are jailing a big dark lake
Three hooks seal the ancient mouth
Keep the east in west and north in south
Is it
Istanbul?
Two watchers on two sides of a creek
Istanbul is located on both sides of the Bosphorus Strait.
They are jailing a big dark lake
Istanbul controls the entrance to the Black Sea.
Three hooks seal the ancient mouth
There are three bridges across the Bosphorus Strait.
Keep the east in west and north in south
Constantinople has historically been an important point of connection between Western and Eastern civilisations, and between Russia and the Middle East.
Not sure of this answer -
Could the city be
Aswan?
Two watchers on two sides of a creek
Possibly the Aswan dam (although why the Nile would be called a creek is beyond me).
They are jailing a big dark lake
Lake Nasser?
Three hooks seal the ancient mouth
????
Keep the east in west and north in south
The Nile flows from south to north. So the ancient Egyptians thought that up(N) was down(S) (on the map). Therefore, E would be W.