Depends on your definition of "pollution". The problem with hydro is that all the good hydro sources are already tapped, and it can lead to significant ecology disruption.
The real clean energy is nuclear fission. We know how to do it, fuel can be reprocessed if you aren't using 1950's light-water tech, and nothing will beat its power-generated-per-acre-of-land ratio.
Depends on your definition of "pollution". The problem with hydro is that all the good hydro sources are already tapped, and it can lead to significant ecology disruption.
The real clean energy is nuclear fission. We know how to do it, fuel can be reprocessed if you aren't using 1950's light-water tech, and nothing will beat its power-generated-per-acre-of-land ratio.