If you want to be nice to the environment, damming (damning?) rivers would intuitively seem like a bad thing for wildlife.

I don't have the details, but when my company went to purchase RECs for 2021 we were told that hydro is no longer considered to be in the level of REC we were targeting (extra green something or other). So the cost for this year was much higher than 2020.

Dumb or not, hydroelectric has its own ecological problems and as the dams near the and of life, the costs associated with that will be most likely "externalized"