Is this man made?

[dilan_randika]

Is this a man made cannel or a natural one? [in red circle] without that black sea will be a lake only

 

[Ramiel]

the photo you added after the edit is Bosporus Canal, which is a natural waterway, but there is a man made project (Istanbul Canal) underway because Bosporus is a huge bottleneck, which also falls into the area of the red circle of your original post.

 

[Jack_Sparrow]

Natural
Bosporus
https://en.wikipedia.org/wiki/Bosporus

 

[imhotep]

Also note that Turkey just started the construction of a canal between the Black Sea and the Sea of Marmara. .... six bridges; 45 kilometres long; 21 metres deep; 30 times safer than the Bosphorus; 90 percent less traffic; six years of construction; a $15 billion budget…