Believe me, I am NO FAN of giant hydro plants; I just didn't know why it would be a particular issue in the tropics and not elsewhere--actually, I guess I still wonder that. Silting is a good explanation for why *any* hydro plant might stop working, but why are the conditions especially that way in the tropics? Maybe the heat makes the rivers sluggish? Or is it just chance that the big powerful rivers that people would tend to want to use for hydro power are in the tropics? Or--?