Plus dams fuck up environment pretty well.
So lakes are bad for the environment? You better not tell Canada or Russia that, seeing as we apparently have something like nearly half the world's accessible fresh water, of which over 80% is in lakes.
Really, the environmental problems caused by dams are caused by poorly planned and managed dams that are overly large and cycled in unfriendly manners. You only get actual issues when you build an overly large reservoir, force the system to have too large of a variance between peak and low flow (one of the problems in several dam systems where they nearly shut off all flow during non-peak power demand times and then open them up too much to produce more power. Causes all sorts of issues just down stream of them.), or provide no reliable means for wildlife to bypass the dam.
A well designed low head dam will pay for itself energy wise in a few months, will use mostly materials taken from on site or near to site for the retaining walls, and will have a usable lifetime of centuries with minimal work to the primary structure.