Even in the long term, it (1) breaks the river into pieces, preventing fish moving up and down, (2) causes silting of the reservoir and lack of silt deposition downstream, and (3) can stress the underlying rock, which is not a great idea in earthquake-proe areas (like northeast China).
Hydro in general might be clean but it is so environmentally destructive :(
you have to weigh the destruction it causes in the short term to the preservation it contributes to in the long term
Even in the long term, it (1) breaks the river into pieces, preventing fish moving up and down, (2) causes silting of the reservoir and lack of silt deposition downstream, and (3) can stress the underlying rock, which is not a great idea in earthquake-proe areas (like northeast China).
in the long term it is another piece in the energy puzzle that prevents the death of all life on earth but i can understand your concerns