Use off under sea currnets and temperature diferents

whoud it be possible to exploit deep sea currents a lot off ocean's have deep cut out trences it whoud be possible to create stops in those trences and build giant turbines working on the the force off the water stream , whe coud also build constant waterflows based on the temperatur diferences between diferent parts off the ocean , it probably whoud costs lots off money , and it whoud need lots off maintenance but the power source is unlimited , and the turbines coud realy have giant proportions , as the currents are verry strong and verry large on somme places , it

I learned about this in my environmental science course in university. I don't remember the details very well but it was said that this is not a good method. It generates too little energy to meet demands.

I could've remembered wrong though. All that I remember clearly is that nuclear fission is the way to go for the near future until nuclear fusion is developed. All other sources of energy are not as effective.