Technical Recommendation 16

Restoring Fish Passage


Since the late 1800s, over 1,000 dams have been constructed in the more than 160,000 square miles of the Columbia River Basin that were historically accessible to anadromous fish. Many Columbia Basin dams completely block fish passage into the watershed’s upper reaches. Dams obstruct passage of salmon and other anadromous fish between spawning and rearing habitat and the Pacific Ocean. Where fish passage was not provided, extirpation of the upstream population was the result. Dams and other water resource developments made more than 55%, or nearly 100,000 square miles, of the historical spawning and rearing habitat unavailable to salmon, lamprey and sturgeon.

Extensive work throughout tributary watersheds has restored passage to over 15,000 square miles of this habitat. The remainder, about 80,000 square miles, is still blocked. (Over the decades, fish agencies, tribes and others have also opened up some 800 square miles of historically inaccessible habitat by providing passage over natural barriers.)

The largest blockages occur in the upper Columbia at Grand Coulee Dam and in the Snake River at the Hells Canyon Complex. Grand Coulee eliminated approximately 1,100 miles of spawning habitat and extirpated the largest number of known anadromous populations relative to other projects (NPCC n.d.).

On the Snake River, the construction of the three-dam Hells Canyon Complex in the 1950s and 1960s blocked nearly 2,000 miles of anadromous fish habitat. Additional spawning habitat was lost following construction of other mainstem and tributary dams. In total over 30% of the habitat originally available to salmon in the Snake River Basin has been lost. The extent of fishing by native peoples also measures the magnitude of damage: Above the four lower Snake River dams, for example, tribal fishers are presently harvesting salmon at less than 1% of pre-contact levels, while no Pacific lamprey are harvested due to extremely low adult returns.

Downstream of Grand Coulee and Hells Canyon dams, salmon and lamprey habitat is also blocked in virtually all the tributaries. Small hydroelectric dams and irrigation diversion dams dot the landscape, excluding or impeding passage to spawning and rearing habitat above. Forestry practices and road building, with inferior design and culverts, create additional blockages to an undeterminable number of tributary streams and habitat miles.

Hypothesis and Needed Actions

Opportunities to restore fish passage are becoming more feasible. Recent developments in juvenile fish passage technology could potentially provide passage opportunities at dams such as Chief Joseph, Grand Coulee, Dworshak and the Hells Canyon Complex.

New passage technology is currently operational and being tested at Round Butte Dam on Oregon’s Deschutes River. In 2012 the U.S. Army Corps of Engineers embarked on passage studies at three high-head dams in Oregon’s Willamette basin and at Howard Hanson Dam in Washington. A new juvenile fish collector is being installed and tested at Swift Reservoir, Washington, and a juvenile sockeye passage facility is now operating successfully at a high-head dam on the Skagit River, Washington. Additionally, the U.S. Geological Survey, U.S. Army Corps of Engineers and U.S. Bureau of Reclamation are investigating and testing new technologies to pass anadromous and resident species more effectively past dams.

The 2011 removal of Condit Dam on the White Salmon River is a significant example of reopening a Columbia Basin river to salmon. See the adjacent White Salmon River Recolonization.

We recommend the following actions to restore fish passage.

  • Continue investigating fish passage technologies and opportunities. Include investigation of fish passage at Chief Joseph, Grand Coulee, Dworshak and Hells Canyon Complex dams as a goal for the Columbia River Treaty 2014/2024 Review process.
  • Assess the feasibility and potential benefits of removing aged and/or unprofitable tributary dams to reopen tributary habitat to anadromous fish.
  • Continue replacing inferior culverts that block or impede salmonid and lamprey passage.
  • Assess habitat quality and reintroduction options in blocked-area passage restoration proposals. Investigate potential donor stocks and evaluate the role and use of supplementation hatcheries.
  • Include above measures to restore passage for lamprey and sturgeon, as applicable.

Expected Outcome

Anadromous fish will return to reopened habitat areas; and eventually tribal members will again be able to harvest these fish at traditional locations that have been blocked for more than a generation.

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