When the dams were built, some watershed impacts were immediate (such as the elimination of salmon stocks in the upper watershed) while some other effects have developed over the last 100 years (such as the sediment deprivation that has impacted the nearshore). Undoing these impacts and bringing back the health of the watershed will likewise take decades to realize once the dams are removed, although some effects will be noticeable in the near term.
Shortly after dam removal, salmon species from the Pacific Ocean will begin to recolonize gradually over 70 miles of habitat that was not accessible to spawning salmon when the dams were in place. Much of this habitat is within the bounds of Olympic National Park and is in excellent condition. It is estimated that within 30 years, the river will produce 300,000 salmon and steelhead combined each year.
After the dams are removed, the Elwha River will regain its natural form and large areas of land that were covered by the reservoirs will be devoid of any vegetation. These riverbank areas will be quickly planted with native plants to begin revegetation.
Since the dams have been shut off in June of 2011, the Elwha River has already created a new path. However, it will take decades to restore portions of that land to the forested landscape that existed prior to the dams.
Some immediate effects will be negative, although they are expected to be short-term. For example, the sediments that were bound behind the dam will begin to migrate down river and eventually out to sea. It is expected this process will take place within 5 years. When the sediment is released initially, it may kill fish and other species in the river and decrease water quality. During that time the House of Salmon will help conserve and repopulate the salmon. Additional restoration actions downstream will help to minimize the impacts from this enormous load of sediment. However, in the long term, the return of the natural flow of sediment will have many positive effects: improving spawning habitat, building up the nearshore area, and reducing the need to build up Ediz Hook artificially.