This is a wild, naive idea. 

Could you submerse a turbine in a place where ocean currents are superficial and strong and tap into its energy?

I have many doubts about this because I know very little about these currents, how fast they, are, the depths, the distance from coast. The turbine would be supported by a floating platform, perhaps be anchored in the seabed if it is possible. It would require a transmission system to send the energy to mainland.

This was inspired by a calculation I did once that estimated the area of the oceans and seas, compared to landmasses. It is a lot of virtually useless space. We should increase, in my opinion, our presence on the waters. Many ideas follow this line.