Although the two dams had helped the development of the local economics, there were several impacts for river environment as well as ecosystem. The first impact was the decrease of the salmon population in the Elwha River. In 1915, more than 23 million eggs were collected from Elwha River salmon and steelhead. However, after the dams were constructed, the number of salmon and other fish began to decrease because there were no fish passage in both Elwha and Gliens Canyon dam. As a result, more than 45 kg of Chinook salmon had not been observed in the Elwha River for many years (See Figure 1). The second impact was sediments. Both two dams had a large amount of sediment and silt blockage. This deposition resulted the erosion of the river banks.