Dam Removals on the Elwha River
The Northwest Fisheries Science Center’s Elwha River Restoration Project provides a unique opportunity to study ecosystem restoration at a watershed scale.
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 Program 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 populations recolonize 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 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 recolonized. But while invertebrate density rapidly rebounded, diversity initially remained low.
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, aquatic food webs' long-term response is an evolving story.
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
Anadromous fish that will benefit from dam removal
Puget Sound Chinook salmon (threatened)
Puget Sound steelhead (threatened)
Olympic Peninsula bull trout (threatened)
Elwha Dam Removal Publications
Acker, S.A., Beechie, T.J. and Shafroth, P.B., 2008. Effects of a natural dam-break flood on geomorphology and vegetation on the Elwha River, Washington, USA. Northwest Science, 82(sp1), pp.210-223.
Brenkman, S.J., Pess, G.R., Torgersen, C.E., Kloehn, K.K., Duda, J.J. and Corbett, S.C., 2008. Predicting recolonization patterns and interactions between potamodromous and anadromous salmonids in response to dam removal in the Elwha River, Washington State, USA. Northwest Science, 82(sp1), pp.91-106.
Brenkman, S.J., Duda, J.J., Torgersen, C.E., Welty, E., Pess, G.R., Peters, R. and McHenry, M.L., 2012. A riverscape perspective of Pacific salmonids and aquatic habitats prior to large‐scale dam removal in the Elwha River, Washington, USA. Fisheries Management and Ecology, 19(1), pp.36-53.
Burke, B.J., Frick, K.E., Moses, R.E. and McHenry, M.L., 2008. Movements by adult coho salmon in the lower Elwha River, Washington. Northwest Science, 82(sp1), pp.119-127.
Coe, H.J., Kiffney, P.M. and Pess, G.R., 2006. A comparison of methods to evaluate the response of periphyton and invertebrates to wood placement in large Pacific coastal rivers. Northwest Science, 80(4), p.298.Coe, H. J., Kiffney, P. M., Pess, G. R., Kloehn, K. K., & McHenry, M. L. 2009. Periphyton and invertebrate response to wood placement in large Pacific coastal rivers. River research and applications, 25(8), 1025-1035.
Duda, J. J., Coe, H. J., Morley, S. A., & Kloehn, K. K. 2011. Establishing spatial trends in water chemistry and stable isotopes (δ15N and δ13C) in the Elwha River prior to dam removal and salmon recolonization. River Research and Applications, 27(10), 1169-1181.
Duda, J., Anderson, J.H., Beirne, M.M., Brenkman, S.J., Crain, P., Mahan, J., McHenry, M., Pess, G., Peters, R. and Winter, B., 2019. Complexities, context, and new information about the Elwha River. Frontiers in Ecology and the Environment, 17(1), pp.10-11.
Duda, J.J., M.S. Hoy, D.M. Chase, G.R. Pess, S.J. Brenkman, M.M. McHenry, and C.O. Ostberg. 2020 Environmental DNA is an effective tool to track recolonizing migratory fish following large-scale dam removal. Environmental DNA. DOI: 10.1002/edn3.134.
East, A.E., Pess, G.R., Bountry, J.A., Magirl, C.S., Ritchie, A.C., Logan, J.B., Randle, T.J., Mastin, M.C., Minear, J.T., Duda, J.J. and Liermann, M.C., 2015. Reprint of: Large-scale dam removal on the Elwha River, Washington, USA: River channel and floodplain geomorphic change. Geomorphology, 246, pp.687-708.
Kloehn, K.K., Beechie, T.J., Morley, S.A., Coe, H.J. and Duda, J.J., 2008. Influence of dams on river-floodplain dynamics in the Elwha River, Washington. Northwest Science, 82(sp1), pp.224-235.
McHenry, M. L., & Pess, G. R. 2008. An overview of monitoring options for assessing the response of salmonids and their aquatic ecosystems in the Elwha River following dam removal. Northwest Science, 82(sp1), 29-47.
McMillan, J.R., R. Pess, G., McHenry, M.L., Moses, R. and Quinn, T.P., 2014. Documentation of unusual, fall spawning by Coastal Cutthroat Trout in the Elwha River system, Washington. Transactions of the American Fisheries Society, 143(6), pp.1605-1611.
McMillan, J.R., Pess, G.R., Liermann, M., Morley, S.A., McHenry, M.L., Campbell, L.A. and Quinn, T.P., 2015. Using redd attributes, fry density, and otolith microchemistry to distinguish the presence of steelhead and rainbow trout in the Elwha River Dam Removal Project. North American Journal of Fisheries Management, 35(5), pp.1019-1033.
Morley, S.A., Duda, J.J., Coe, H.J., Kloehn, K.K. and McHenry, M.L., 2008. Benthic invertebrates and periphyton in the Elwha River basin: current conditions and predicted response to dam removal. Northwest Science, 82(sp1), pp.179-196.
Morley, S.A., Coe, H.J., Duda, J.J., Dunphy, L.S., McHenry, M.L., Beckman, B.R., Elofson, M., Sampson, E.M. and Ward, L., 2016. Seasonal variation exceeds effects of salmon carcass additions on benthic food webs in the Elwha River. Ecosphere, 7(8), p.e01422.
Morley, S.A., Foley, M.M., Duda, J.J., Beirne, M.M., Paradis, R.L., Johnson, R.C., McHenry, M.L., Elofson, M., Sampson, E.M., McCoy, R.E. and Stapleton, J., 2020. Shifting food web structure during dam removal—Disturbance and recovery during a major restoration action. PloS one, 15(9), p.e0239198.
Moser, M.L. and Paradis, R.L., 2017. Pacific lamprey restoration in the Elwha River drainage following dam removals. Am Curr, 42, pp.3-8.
Liermann, M., Pess, G., McHenry, M., McMillan, J., Elofson, M., Bennett, T. and Moses, R., 2017. Relocation and recolonization of coho salmon in two tributaries to the Elwha River: Implications for management and monitoring. Transactions of the American Fisheries Society, 146(5), pp.955-966.
Pess, G. R., McHenry, M. L., Beechie, T. J., & Davies, J. 2008. Biological impacts of the Elwha River dams and potential salmonid responses to dam removal. Northwest Science, 82(sp1), 72-90.
Pess, G.R., Liermann, M.C., McHenry, M.L., Peters, R.J. and Bennett, T.R., 2012. Juvenile salmon response to the placement of engineered log jams (ELJs) in the Elwha River, Washington State, USA. River Research and Applications, 28(7), pp.872-881.
Peters, R.J., Liermann, M., McHenry, M.L., Bakke, P. and Pess, G.R., 2017. Changes in streambed composition in salmonid spawning habitat of the Elwha River during dam removal. JAWRA Journal of the American Water Resources Association, 53(4), pp.871-885.
Quinn, T.P., Bond, M.H., Brenkman, S.J., Paradis, R. and Peters, R.J., 2017. Re-awakening dormant life history variation: stable isotopes indicate anadromy in bull trout following dam removal on the Elwha River, Washington. Environmental Biology of Fishes, 100(12), pp.1659-1671.
Ritchie, A.C., Warrick, J.A., East, A.E., Magirl, C.S., Stevens, A.W., Bountry, J.A., Randle, T.J., Curran, C.A., Hilldale, R.C., Duda, J.J. and Gelfenbaum, G.R., 2018. Morphodynamic evolution following sediment release from the world’s largest dam removal. Scientific reports, 8(1), pp.1-13.
Roni P, McHenry M, Pess G, Beechie T. Evaluating changes in salmon spawning habitat and spawners in the Elwha River following dam removal. In American Fisheries Society Symposium 2008 (Vol. 65, pp. 000-000).
Tonra, C. M., Sager-Fradkin, K., Morley, S. A., Duda, J. J., & Marra, P. P. 2015. The rapid return of marine-derived nutrients to a freshwater food web following dam removal. Biological Conservation, 192, 130-134.
Warrick, J.A., Bountry, J.A., East, A.E., Magirl, C.S., Randle, T.J., Gelfenbaum, G., Ritchie, A.C., Pess, G.R., Leung, V. and Duda, J.J., 2015. Large-scale dam removal on the Elwha River, Washington, USA: Source-to-sink sediment budget and synthesis. Geomorphology, 246, pp.729-750.