In the 9th century, long, long before Nicola Tesla, the vikings of Iceland changed the course of the Öxá, to create a waterfall in þingvellir. The sagas tell that it was named after a troll that used to chop up early parliamentarians with an axe — surely a witty reference to early spiritual struggles in Iceland, which was grounded simultaneously by at least three spiritual traditions: Norse, Irish and Christian. Wikipedia tells how the waterfall was used to provision campers with water.I will merely point out a couple things. First, the Icelandic killing fields were in this river, either by the drowning of witches, ie reunion with the troll, or by beheading on a rock in the water, ie the cancellation of Christian belonging, as a form of organic justice. This was hydro power before the industrial age. We now call it “nature” and “beauty.” Those are only industrial terms. Beware.