Freeing the Elwha: Science Unit 3

Challenges and Opportunities for Restoration

Lesson 14: Impact of Hydroelectric Dams on Salmon

Guiding Question: Dams are important to people but they have a serious impact on salmon migration. How do dams affect salmon and what successes have people had in trying to help salmon migration?

Overview: This lesson focuses on the impacts that hydroelectric dams have had on anadromous salmon migration and some of the mitigation techniques that have been designed to reduce these impacts. Hydroelectric projects were started during the Great Depression and continued through the 1960's and 1970's for the purpose of channeling water for irrigation in the arid Columbia Basin and to generate cheap electricity. However, the dams created obstructions for migrating salmon. Even those dams built with fish passage, such as fish ladders and navigation canals, have had major impacts on the survivorship of juvenile salmon due to mortality in the turbines and spillways, increased water temperatures, predation, and a myriad of other factors.

Time: One class period


Lesson 15: Effects of Elwha Dams on Salmon

Guiding Question: The building of the Elwha River Dams had a huge impact on the anadromous fish of the Elwha River, why were the dams built in the first place, how have they affected anadromous fish and the surrounding environment, and why are they coming down?

Overview: This lesson focuses on the impacts that the building of the two dams on the Elwha River had on anadromous fish species, including the loss of 70 miles of river habitat for migrating fish, the effects of sediment loss on spawning grounds downstream, and general habitat degradation downstream. Learn about pre-dam conditions both in-river and in the surrounding terrestrial environment. Then hear the story of Thomas Aldwell, the entrepreneur who built the first dam and refused to accommodate fish. Finally, discuss the political and environmental conditions that led to the decision to remove the dams.

Time: Two class periods


Lesson 16: Restoring the Elwha River

Guiding Question: There are many important factors involved in removing the Elwha Dams and restoring the Elwha River. What strategies is Olympic National Park employing to help the river and its anadromous fish recover?

Overview: This lesson focuses on the plans to remove the dams, restore the river, and return salmon to the Elwha River watershed. Managers will have to use different strategies depending on the current population levels, life histories, and habitat requirements for each species of salmon, to ensure recovery. Some species will be able to naturally recolonize the river and return to anadromy. During the dam removal process, there is expected to be great amounts of sediment released from the deltas which have formed at the mouth of the reservoirs. To assure their survival, some salmonid species will be stored and propagated in hatcheries, protected from the high levels of suspended sediment. Some species will need to be out-planted up river to facilitate recolonization following dam removal. In addition, a great deal of ecological work will be necessary post dam removal to restore vegetation, engineer logjams, and return the sediment regime to form spawning beds.

Time: One class period


Lesson 17: Hatcheries, Saviors or Scourge for Wild Salmon?

Guiding Question: Hatcheries seem like a good idea, but they are fraught with problems - how are hatcheries both a danger and a blessing to wild fish?

Overview: This lesson focuses on the history and roles that hatcheries serve in sustaining commercial fisheries, native fish populations, and saving endangered fish stocks. Hatcheries were historically a popular tool for propagating large numbers of fish for sustaining commercial fisheries, however, a series of problems have resulted in increasing controversies over their use. Some of the problems include the use of non-native stocks, the development of non-competitive behaviors, and over-stocking fish beyond the natural carrying capacity of the environment at the expense of wild native fish. However, as wild fish runs become threatened with extinction, hatcheries are also proving to be a valuable tool for saving these wild native runs.

Time: Two class periods


Lesson 18: Over-Fishing and Fisheries Collapses

Guiding Question: What factors have led to the collapse of marine fisheries around the world?

Overview: This lesson focuses on the recent collapse of marine fisheries across the world due to increased commercial fishing pressures, a result of increased technology coupled with the changing climate of marine environments related to greenhouse gas pollution. Collapsed fisheries include Pacific salmon, Atlantic cod, and Orange Roughy, among others. The collapse of these fisheries has resulted in dramatic shifts in food webs and ecological processes at sea and on terrestrial ecosystems. In addition, it has had major impacts on human coastal communities.


Lesson 19: Salmon Farming; Potential and Problems

Guiding Question: Salmon farms seem like an ideal solution for helping wild salmon and increasing the worldwide demand for salmon production, what are the problems associated with salmon farming and are there ways of solving these problems?

Overview: This lesson focuses on the economic and ecological values and costs of salmon farming. Salmon farms have been seen by many as an opportunity to help wild salmon runs, by producing fish to meet increased worldwide demand for salmon and taking some of the pressures off wild salmon by commercial fisheries. However, salmon farms have developed several serious ecological and economic problems that must be addressed. Escaped salmon from farms represent competition for food resources and spawning grounds. Their dense populations are susceptible to disease outbreaks and parasite infestations. Their food contains high concentrations of chemicals such as PCB's and mercury which bioaccumulate in their bodies and contaminate the nearby environments.

Time: One day for presentation plus research and writing time as needed



This webpage was made possible in part by a grant from Washington's National Park Fund.

Last updated: April 6, 2015

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