Summer 2024 was an unusual summer in an unusual year for salmon in California’s Central Valley.

July 2024 was the hottest ever recorded on earth and in the Central Valley.  Record high air temperatures occurred in early July throughout the Valley.  A close look at July 2024 provides some valuable insights as to the future climate and salmon in the Valley.

July is an important month for Chinook salmon populations in the reaches of the rivers that are downstream of major dams.  Winter-run salmon are at peak spawning in the Sacramento River near Redding (mainly the ten miles below Keswick Dam).  Spring-run salmon are holding over the summer in the Trinity River below Lewiston Dam, in the Sacramento River below Keswick Dam, and in Clear Creek below Whiskeytown Dam.   (Spring-run salmon are also holding in the Feather River below Oroville Dam and below falls on Butte, Deer, and Mill creeks.)  Fall-run salmon have only just begun their journey from the ocean in the Sacramento and Klamath/Trinity rivers.

The goal in summer for the Shasta/Trinity Division of the federal Central Valley Project is to keep dam releases cold (around 50-52^oF) for winter-run spawning and egg incubation, and for holding adult spring-run salmon.  Dam releases from the stored cold-water-pool supply are prescribed to accomplish the goal.  The dams also release water for hydropower, for downstream water supply deliveries, and to meet requirements for salmon habitat and other environmental purposes.

Reclamation must balance these uses in July with protecting the salmon and other fish during the rest of the water year and with maintaining adequate storage for next water year.  Reclamation released its draft environmental impact statement for the future long-term operations of the Central Valley Project operating earlier this summer – comments were due in September.  Reclamation’s plan is not to meet the needs of the salmon except in wetter years – simply put, to “split the baby.”  Reclamation’s proposal for how it will balance the needs of water users and the salmon will lead to the extinction of at least two runs of the salmon.

In the Central Valley, Water Year 2024 turned out to be above normal, after a wet 2023.  Shasta and Trinity reservoirs nearly filled during the winter-spring – a good start to end-of-spring conditions.  Shasta Lake started July with 4 million acre-feet (maf) in storage (out of a 4.5 maf capacity) and ended July with storage of 3.5 maf (Figures 1 and 2).  Trinity Lake began and ended July with 2 maf in storage (out of a 2.5 maf capacity), after transferring about 100 thousand acre-feet (taf) to the Sacramento River in May-June and another 100 taf in July.  Water temperatures of released water from both Keswick and Lewiston dams were maintained at the target 50-52^oF.  The secret to this success was retention of sufficient storage and cold-water pool supplies in Shasta and Trinity reservoirs – a relatively easy task in an above normal water year after a wet year.

The challenge for Reclamation in the past, present, and future is to retain sufficient storage and cold-water-pool supplies to maintain the 50-52^oF dam release targets through the fall of all water year types, especially the drier years.  Reclamation tried in the 2021-2022 drought, but grievously failed to meet the needs of salmon (Figures 2-4).  Now Reclamation is asking the state and federal resources agencies for permission to explicitly plan to not meet the needs of the salmon in drier years.

Absent such an agreement to fail in drier years, Reclamation will have to reduce hydropower production/revenues and, most critically, the amount of irrigation deliveries to water contractors.  It will have to reduce already dry-year-constrained water deliveries to retain more stored water and the necessary cold-water-pool supply for salmon.  It will have to carry over more storage supply at the end of summer, have greater amounts stored by the end of spring, and deliver less water in many years from spring through fall.  There is no choice if Reclamation is to meet promises and commitments to maintain the salmon populations in the Klamath/Trinity and Central Valley.

For a more insight on what the plan entails and how better to meet the needs of salmon, see CSPA’s alternative plan submitted in 2021 to save salmon in a drought year like 2021.

https://www.waterboards.ca.gov/drought/sacramento_river/docs/2021/cspa_tmp_052321.pdf

See also NGO comments (joined and partially written by CSPA) on the Draft Environmental Impact Statement for the Long-Term Operations of the Central Valley Project and State Water Project.

Figure 1. July 2024 conditions in the Shasta-Trinity Division of the CVP. Blue numbers are streamflows (cfs) and reservoir water storage levels. Green numbers are average water temperatures (degrees F).

Figure 2. May-October Shasta Reservoir storage levels in acre-feet 2021-2024.

Figure 3. Trinity River flows and water temperatures below Lewiston Dam 2020-2024.

Figure 4. Water temperature of Sacramento River below Keswick Dam 2021-2024. Note the cold-water-pool supply in Shasta Reservoir was depleted by the send of August in drought years 2021 and 2022 despite attempts to conserve the supply in spring by releasing warmer surface waters from the reservoir.