to talk about hide ro electricity and the possibility that we might get some more of it is oskar sigvaldason, and he is an engineer who spent a lifetime of falling water, one might say. welcome to the broadcast. have all the dams been built? are we built up on hydro? are there any other possibilities? >> based on an estimates carried out a few years ago, it's estimated that about 30% of the economically, potentially developable hydro has now been constructed. there's at least 2/3 that has not been developed yet and that figure is probably conservative. >> environmentalists have turned against hydro, have they not? i have people in the american west who would like to take all the dams down and return to nature. they don't know what they'll do for electricity or certainly for recreation. >> there was a move certainly in the 1990's very much driven by environmentalists, which was really bringing to an end large dam construction, and with that meant large hydroelectric developments, which led to the commission carried out into the early part of this decade that really in many ways served to over