I’ve worked on about 30 different run of river hydro electric projects over the last 15 years. Yes there is some environmental impact but the ones I have worked on have had a team of biologists and years of environmental studies and they would never result in a dead fish any more often that the river would have naturally by itself. If any habitat is destroyed they have to create new habitat such as spawning channels. They probably spend 10%-20% of the entire budget on environmental. These run of river plants don’t flood more than 1000m^2 area, use a weir instead of a dam, leave water in all sections of the river channel, and don’t cause unnatural changes in the river level at a rate greater than 1” per hour which is a very conservative rate compared to what the rivers of this size and nature naturally do by themselves when it rains or melts.

I know you said Dams and not weirs and not run of river plants, and big dams have their issues, but not on the same scale as the oil industry.