Drying the Mediterranean Sea is surely a bad idea, but I wonder why nobody ever built hydroelectric generators into the Strait of Gibraltar.
There is a huge steady flow of surface water from the Atlantic into the Mediterranean (1 million cubic meters per second), and almost as much flows back into the Atlantic in deeper layers.
Why not tap into these streams to generate electricity?
Tidal energy is expensive - sea water is very corrosive and under water maintenance access isn't cheaply solved. Also you need to retain access for ships and subs.
The UK has the second highest tidal ranges in the world and is probably a world leader, we still generate nearly no energy from tidal.
