[ska]

Due to silting, most hydro isn't really renewable either iiuc. It's just looks that way for long enough that we tend to talk about it that way.

[snowwindwaves]

Reservoirs filling with silt may reduce storage which would turn the dam in to a run of river plant. Less control over when the electricity is made. Also reservoirs could be dredged out to allow the silt to continue its way downstream.