They aren't worth keeping, either. The PG&E Feather River project for example can be replaced by a cheap mid-sized PV farm. Those run-of-the-river hydroelectric projects are way too dangerous to keep around which I think is best exemplified by the fact that the Feather River project started the largest wildfire in California history. So on the one hand you have the almost negligible benefit of an unreliable, seasonal power source and on the other hand you have the extirpation of salmon and a million acres of burnt forests. I known which one I prefer.