Large dams deplete fisheries, harm fish spawns, damage ecosystems, recede coastlines and many other problems linked to damming of our river systems. Not only do they destroy the environment, it appears they also do not make economic sense. The actual construction costs are too high to actually produce a positive return. In addition, they take an extremely long time to build thus making them useless in a crucial energy emergency and the longer the project is delayed the more money is wasted. In other words, dams are uneconomic.