[zokier]

The damage of hydro is fairly localized afaik, both spatially and temporally. Fossil fuels cause damage globally (in addition to the local damage of oil fields/coal mines, and the power plants), and the damage is much more long lasting. Also the damage of hydro does not accumulate over time afaik.

[maxerickson]

Hydro plants have huge impacts on stream and river ecosystems. A good case study would be the impact on salmon in the pacific northwest of the U.S.