Hydroelectric energy is very cheap
Maybe, if you don't factor in the future costs of the damn when it becomes end-of-life ... and the consequences.
There was something I read about hydro-electric that suggested it wasn't the panacea people imagine, probably todo with pumping the water back up and it therefore only really acting as a store of energy (like a huge battery) but no system is 100% efficient so there is a lot of wasted energy so the net gains are not as great as people imagine and they have a huge environmental footprint.