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Following the removal of four hydroelectric dams in 2024 – the largest such project in US history – the Klamath River flowed unimpeded below the Keno Dam for the first time in 102 years, and miles of historical spawning grounds became freely accessible to migrating salmon and steelhead trout. However, the freshly accessible habitat raises new questions for resource managers about how to optimize waterflows in the changing river basin to support both fish and people. 

Balancing water needs for people and fish is critical in the Klamath Basin, an area with significant agriculture. While four dams have been removed, water allocation and flow control still occur at dams and other diversion sites in the upper regions of the Klamath. With knowledge of how and when fish use the river, water managers can identify when to continue flushing flows to support fish survival or reduce flow and reallocate the water elsewhere with minimal impact to fish populations.

With partners from the Yurok, Hoopa, and Karuk Tribes, WFRC is working to assess the connection between varying controlled river flows and the survival of juvenile Chinook salmon as they voyage to the ocean in a process known as outmigration. The five-year long study investigates how juvenile Chinook use habitat under different water flow management regimes before and after dam removal. 

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Beginning in 2023, scientists have released about 800 juvenile Chinook below the Iron Gate Dam annually. As the fish move down the river, scientists track their movement using a combination of acoustic transmitters implanted in fish and strategically placed acoustic receivers throughout the river. High-resolution models are then used to triangulate fish positions and determine when, where, and how long young Chinook of varying sizes and ages occupy different parts of the riverscape and how this is changing after dam removal. For example, scientists are interested to know if newly hatched fish migrate more slowly and use riverbanks and riverside habitats more than juvenile fish that already lived in the river for a year, and whether changes to flows affect access to those habitats. They are also interested in the movement of larger juvenile Chinook under different flow rates relative to the duration they stay in areas of the river where the parasite, Ceratonova shasta, is present. Historically, low water flows have increased the likelihood that Ceratonova shasta infect juvenile Chinook and lower their survival.

In another study, WFRC scientists have been monitoring adult coho and Chinook salmon movement as the fish approach and pass Keno Dam. Keno Dam was recently taken over by the Bureau of Reclamation from PacifiCorp after the lower hydroelectric dams were removed. While it was built long ago in 1967, it was not until the four lower dams were removed last year that salmon could reach Keno Dam and potentially use the fish ladder to reach additional habitat in the Upper Klamath Basin. WFRC scientists deployed acoustic and video cameras to monitor returning coho and fall-run Chinook salmon as they approached and moved up the fish ladder. Acoustic cameras, much like the fish finders used by fishermen, capture fish movement while video cameras provide visual confirmation. Data from these cameras are currently being analyzed to determine how the salmon performed.

As we adjust to a new normal in the Klamath River Basin with the four lower river dams removed, our research at WFRC will continue to play an important role informing actions related to water and ecosystem management.