When dams were first built, fish experts recognized the potential for fish not being able to return upstream to spawn. In response to this problem, fish ladders were created. This allowed adult fish to get from the ocean to fresh water and lay their eggs, however, the journey for maturing salmon from rivers to the ocean is where the problem still lies. Dams create reservoirs due to the slowing of river currents. These reservoirs are deep and young salmon can easily get lost, making them the perfect meal for predators that live there and know their way around the water. Those that do make it through reservoirs alive then have to deal with turbines, spun by the flow of the water. Many salmon are pushed through the turbines by the water. Spinning blades and high levels of water pressure kill many before they make it to the other side. Reservoirs and turbines kill between 5 and 15% of migrating salmon, and it is estimated that this day in age, in the Columbia and Snake rivers alone, each salmon must travel through four to eight dams before reaching the ocean. 80-95% of the salmon that have traveled through all eight dams will be killed. The picture to the left shows how turbines can chop fish up.For more information click the link below:
http://www.nwenergy.org/outreach/fact/dams_whydams.html
