Thank you very much for the additional info sir!
I agree with that, If not I'm wrong it's because of siltation. As time flies sediment deposits build up under the dam making the it shallower.
Yes there's no such thing as a perfect energy source. We have no choice but to pick the better ones and improve it along the way.
Again, many thanks to you guys in @steemstem and @curie! You're all awesome. XD