Dam Removals on the Elwha River

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History of the Elwha Dam

In the early 1900s, two hydroelectric dams were constructed on the Elwha River in Washington State: the 32-m high Elwha Dam and the 64-m high Glines Canyon Dam. For over a century, these dams blocked anadromous fish from accessing over 90% of the watershed. The dams also blocked the natural delivery of sediment and wood to downstream habitats,

After decades of lobbying by the Lower Elwha Klallam Tribe and allies, Congress passed the Elwha River Ecosystem and Restoration Act. Both dams were removed simultaneously over three years from 2011 to 2014—re-opening more than 70 miles of pristine salmon habitat. Dam removals of such magnitude had never been undertaken before.

Understanding the ecological effects of dam removals

Researchers in our Watershed and Ecosystem Analysis programs work with the Lower Elwha Klallam Tribe and other partners such as Olympic National Park to study this historic undertaking's ecological significance. Together, we are examining how riverine, estuarine, and nearshore habitats are changing due to dam removal, and what this means to the entire Elwha ecosystem. Without this complete story, we will miss an opportunity to understand our river systems better, manage our fisheries, and inform future dam removals.

One of our first steps was to examine how dams altered fisheries and ecosystem function. Studies conducted before the removal of the dams provided critical baseline data to help interpret ecosystem changes. We are now actively collecting additional information to monitor the river system's response as anadromous fish repopulate the upper watershed. Our results demonstrate the critical importance of maintaining longitudinal connectivity to support watershed processes and ecosystem services.

Understanding changes to fish populations

Once one of the Olympic Peninsula's most productive salmon rivers, the dams reduced the Elwha River's salmon abundance to a fraction of its former levels. With the barriers removed, aquatic organisms regained access to the entire river. Anadromous fish such as salmon returned to areas that have been void of such species for a century. 

This free passage has also prompted a rapid increase in salmon life history diversity. One example is the "re-awakening" of summer steelhead, which is likely originating from up-river resident O. mykiss populations. Species such as Pacific lamprey are also increasing following dam removal. We continue to monitor changes to fish population levels, life history diversity, growth, and survival.

Understanding changes to aquatic food webs

In large rivers, algae is a primary food source for higher trophic levels, such as benthic invertebrates. These invertebrates are, in turn, an important food source for young salmon. When adult salmon return from the ocean to spawn, their bodies carry marine nutrients that help sustain primary production and thus complete the cycle.  

Before the dams' removal, these marine-derived nutrient levels and the associated invertebrate diversity were lower above the dams than they were below. During active dam removal, highly elevated suspended sediment concentrations strongly depressed benthic invertebrate density and diversity below the dams. As the river returned to background turbidity levels, generalist taxa with rapid life cycles quickly recovered. But while invertebrate density rapidly rebounded, diversity initially remained low with fewer types of taxa. 

We continue to examine how dam removal affects nutrient levels, primary production, and benthic invertebrates across the Elwha watershed. With physical habitat complexity increasing below the former dams and salmon populations increasing above, the long term response of aquatic food webs continues to evolve. 

Partners

Lower Elwha Klallam Tribe

National Park Service – Olympic National Park

United State Bureau of Reclamation

United States Fish and Wildlife Service

United States Geological Survey

University of Washington

Washington Department of Fish and Wildlife

Trout Unlimited

The Conservation Angler

Anadromous fish that will benefit from dam removal

Puget Sound Chinook salmon (threatened)

Puget Sound steelhead (threatened)

Olympic Peninsula bull trout (threatened)

Chum salmon

pink salmon

coho salmon

Eulachon (threatened)

Pacific Lamprey