Hydro is the most ecologically damaging for the site (it tends to wipe out an entire ecosystem for many miles).
As long as you don't care about proliferation danger (by militarizing staff and the site), you can reprocess and burn spent nuclear fuel in breeder reactors/reprocessors.
Hydro is indeed as you say. Also, surprisingly to many, a big source of CO2.
Nuclear is high-variance in the ecological damage: 99.25% are basically fine, and those other three are (1) Three Mile Island; (2) Fukushima, more an embarrassing mistake than anything else, as the deaths and environmental damage due to the plant was far less than deaths and environmental damage due to the tsunami that also damaged the plant; and (3) Chernobyl.
It is simultaneously true that (1) even including Chernobyl, the amortised cost of handling nuclear disasters does not add much to the cost of the electricity; and (2) the cost of handling the disaster probably played a large part in the collapse of the Soviet Union.
> least ecologicially destructive (by far)
On average. The long tail doesn't look so great.