Historically one of the most productive salmon-producing rivers in the Puget Sound, the 45-mile-long Elwha River was once home to 10 salmon runs. Estimates suggest that nearly 144,000 Chinook, coho, pink, chum and sockeye salmon, once freely spawned throughout Washington State’s Elwha Basin. However, the construction of two dams on the Elwha River more than 90 years ago dramatically changed the river’s ecology. Containing no passage facilities for fish, the Elwha and Glines Canyon dams blocked the salmon from migrating upriver to spawn. The lower Elwha Dam confined salmon to the lower 5 miles of the river; and over time, a dramatic decline in fish populations occurred. Today, the Elwha Chinook, steelhead and bull trout are federally threatened species under the Endangered Species Act.

Now, with the impending removal of the dams, researchers have a unique opportunity to study the effects that freeing the river will have on the salmon and their habitat. However, to do so, they must first gather comprehensive information on the ecosystem as it is now.

The ecological effects of both dams on the Elwha ecosystem have been large and cumulative. They have not only prevented salmon from spawning upstream but also have prevented important sediments from flowing downstream. The dams have formed two reservoirs, Lake Mills and Lake Aldwell, which have trapped enough sediment to fill a professional football stadium to the roof six times. The capture of 17.8 million cubic yards of sediment has starved the river of material that would have naturally accumulated downstream and receded as part of a normal seasonal process. Biologically productive areas, such as the delta at the river mouth and nearshore beach areas, were particularly affected. The result of starving the river of its sediment has been erosion in nearshore areas of the Strait of Juan de Fuca and an armoring of the river bed, which have reduced the areas available for salmon to spawn.

Where wild pink salmon were once common in the lower river, now hatchery-produced Chinook and coho salmon are the most numerous of the returning adult salmon. The loss of the marine-derived nutrients that historical runs of salmon brought with them upriver may have affected aquatic communities between the dams and above the upper dam. This lack of salmon nutrients may also have effects extending into riparian and upland areas. Many species of birds and mammals who once feasted upon salmon that lay dead or dying after spawning may have suffered population declines.

In 1992, to help restore migratory fishes such as salmon and trout, Congress passed the Elwha River Ecosystem and Fisheries Restoration Act. This Act placed the Department of the Interior in charge of the “full restoration of the native anadromous fisheries” of the river. After extensive analysis, the department determined the removal of both dams would best accomplish that goal.

For researchers, the impending removal of the dams and the restoration of the Elwha River present unique study opportunities:

• Removal of the 108-foot Elwha Dam and the 210-foot-tall Glines Canyon Dam to restore the watershed is the largest decommissioning project in history.
• The watershed above the dam is a protected area within Olympic National Park, making it an ideal setting to study the effectiveness of river-restoration techniques.
• The restoration of the river could have far-reaching effects, from the revival of salmon runs to “jumpstarting” a whole ecosystem that depends on salmon-borne nutrients.

Researchers are seizing the opportunity to track the return of salmon and to study changes in the ecosystem after dam removal. Federal and state agencies, the Lower Elwha Klallam Tribe and universities have accelerated their research and monitoring activities in these areas. Baseline information they are collecting will represent the existing conditions of a river ecosystem that dramatically changed more than 90 years ago with the dams’ construction.

A recent example of data collection that has taken place is a large-scale survey of adult fish in the main-stem Elwha River from headwaters to the sea. Researchers conducted an underwater snorkel survey, one of the longest in North America, during August 2007. The 42-mile survey began at 2,250 feet in the upper Elwha Valley and ended at the sea where the river enters the Strait of Juan de Fuca. Biologists from the following organizations participated:

• National Park Service
• Lower Elwha Klallam Tribe
• U.S. Fish and Wildlife Service
• U.S. Geological Survey
• National Oceanic and Atmospheric Administration - Fisheries
• Peninsula College
• Wild Salmon Center

Unlike similar whole-river efforts that may occur over an entire summer, this survey of the Elwha River took place in a single week. Because biologists surveyed such a large wilderness river over such a short period of time, this survey represents a one-of-a-kind effort. The goals of the survey follow:

• Establish the baseline of adult fish distribution and patterns of abundance for each species throughout the entire river.
• Increase collaborative efforts among researchers working in the basin.  

In order to cover such a long distance and large area, the expedition required 21 divers and aerial reconnaissance surveys to scout hazardous areas in canyons. When surveying the remote locations in the upper Elwha River basin, biologists used a string of mules to haul 1,000 pounds of fisheries sampling and camping equipment. The survey followed in the footsteps of an earlier whole-river effort the USGS Western Fisheries Research Center personnel conducted during the summer of 1995. Currently, biologists are analyzing the data they collected in 2007 and planning for similar efforts prior to dam removal.

So far, biologists have determined that the presence of salmon below the dams has contributed to higher species richness than in sections between or above the dams. They also learned high-quality habitat awaits returning salmon in Olympic National Park. Preliminary results have revealed much-needed information on fish populations in the river:

• In the 5 miles below the dams, divers observed Chinook, pink, and coho salmon, along with bull trout, threespine stickleback, and starry flounder.
• Above the dams, biologists observed only rainbow trout and bull trout.
• Between the dams, they observed rainbow trout, bull trout and non-native brook trout.

• In total, the divers observed 7,300 rainbow trout, 215 bull trout, 539 Chinook salmon and 26 pink salmon.  

By establishing a fish-population baseline, this landmark study will answer research questions on how resident populations above the dam will interact with re-colonizing salmon populations. It will also help scientists measure the overall recovery of salmon following the removal of the dam.

Interior expects to begin removing the dams in 2012. Dam deconstruction will begin after it completes the construction currently underway to maintain the domestic water supply of Port Angeles. Meanwhile, USGS scientists and their research partners will continue to document the existing ecological conditions prior to dam removal. Once dam removal begins, researchers will monitor changes in the free-flowing river as salmon once again swim upriver to spawn.