Well, in this case the flooded area was under water before as well... just frozen water. So I assume the environmental impact would be small, here.

Also I would assume, the higher up the mountain the dam is build the smaller the impact due to less flora and fauna.

I'd argue though that the 500 in Fukushima's case don't include the ripple effect of dying fish, hurting the environment and making products more radioactive, which then get shipped all over and cause cancer in people (I'm exaggerating but you get the gist).

While the death toll of nuclear accidents is relatively low, their economic cost seems to be staggering. The Japanese authorities enforced a 30km exclusion zone around Fukushima; if an accident of similar size had happened to the Beznau nuclear plant, the entire city of Zürich could have fallen inside the exclusion zone. Just think of the real estate value vaporized. Even if it's one event in a thousand years, I'm not sure it's worth the risk.

The number 500 is a very rough estimate. The vast majority of deaths considered to be related to the nuclear failure involved old people who had to be evacuated, and then died due to stresses or medical problems during the evacuation. The number of deaths attributed to actual radiation exposure is ONE.

Fourth, hydropower has claimed for more lives than nuclear power from direct accidents (remember that Fukushima has killed 0) [1].

[1] https://www.oecd-nea.org/ndd/reports/2010/nea6861-comparing-...

Nuclear plants need a large supply of cooling water, so they are almost all near rivers, seas or lakes.