What could happen if black sea was a freshwater lake?

To be correct, the black sea was NOT a freshwater lake. Lakes without overflow quickly become salt lakes, like Caspian sea. If you close the Bosporus, Russia lost the southern sea ports, 1 fleet, and many trade (Romania and Ukraine too). read more

Before that date, glacial meltwater had turned the Black and Caspian Seas into vast freshwater lakes draining into the Aegean Sea. As glaciers retreated, some of the rivers emptying into the Black Sea declined in volume and changed course to drain into the North Sea. read more

The Black Sea is a sea that has been a lake in the past. It is currently connected to the Mediterranean and receives an inflow of salt water through the Dardanelles and Bosporus. During times of lower water levels, the Black Sea and Mediterranean Sea were not connected and the Black Sea was effectively a lake. read more