Dams really aren't environmentally friendly in the way many people assume they are.
Compare that to what are considered massive world news nuclear power plant tragedies like Chernobyl (about 31 direct deaths, long term effects are up for debate: https://en.wikipedia.org/wiki/Deaths_due_to_the_Chernobyl_di...) and Fukushima (1 direct death, low counts of radiation poisoning that can be attributed to it: https://en.wikipedia.org/wiki/Fukushima_Daiichi_nuclear_disa... ).
Not to be pedantic, but...
Neither can many other pollutants, but it can easily be detected, in fact it's probably one of the most easily detected.
If the choice is between environmental damage from fracking or coal mining and deaths from coal pollution or flooding a valley somewhere...