Hydroelectric dams can be tremendous power generation solutions, relatively sustainable compared to other options. However, old unused or inefficient dams can be removed in favor of more modern options. When river dams are removed, salmon re-enter breeding grounds very quickly. A similar thing was previously observed when the Elwha River dams were removed as well. This leads to myriad ecosystem revitalization effects. https://youtu.be/Q3ooEH3cGHs?is=dtfbFdDcFe5zYeFU