Clean or cleaner than coal? Lets not forget that the waterlevel in the reservoirs is not constant, it fluctuates depending on the season and desired energy output of the damn at a given time.
The bottom of the reservoir is mostly void of vegetation capable of stopping wind erosion so when the surface lowers you get prime conditions for sandstorms which can easily destroy nearby vegetation. A problem being created in Iceland as we speak.
Of course it is possible to improve the landscape with dams and geothermal plants but it is a very tricky business.