Modern dams are marvels of engineering but after decades of neglect the U.S. infrastructure is in crisis and by 2020, 85% of U.S. dams may be near their breaking point. When the South Fork Dam near Johnstown, Pennsylvania gave way in a storm in 1889, killing 2200 people, it was the worst disaster in U.S. history. Today, with millions of Americans living nearby massive dams, the result of a failure could be catastrophic.