thanks for highlighting all the environmental impacts of Hydroelectricity, there is always a trade-off with most things in life, but a pristine untouched wilderness, can be devastated by the construction of a damn, so sometimes the environmental costs outweigh the benefits.

One other development which is common now, is pumped hydro, where the water is pumped back up to the damn using off peak power (when electricity is cheap) and then generating the electricity during peak times. This is effectively a battery, and is a really good addition to an electricity grid particularly with wind and solar which aren't generating all the time.