In a 10/19/2023 post, I discussed how the lack of access to Folsom’s deep cold-water-pool results in delayed natural and hatchery spawning of American River fall-run salmon. During the 2020-2022 drought, Reclamation released water from the lower-level power bypass to provide the cold water (<55ºF) salmon need for spawning (see Figure 1). However, this fall 2024 Reclamation has chosen not to use the power bypass to release cold water (Figure 2), despite higher storage levels than during the recent drought (Figure 3). Lack of cold water delays natural spawning and hatchery egg taking, to the detriment of egg viability and fry production.
Figure 1. Water temperature of water released from Folsom Dam, Oct-Nov 2021. Late October drop in water temperature was from release of cold water from lower level outlet. Also shown is recent average for previous 7 years.
Figure 2. Water temperature of water released from Folsom Dam, Oct-Nov 2024.
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 50-52oF) 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 50-52oF. 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 50-52oF 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.
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.
The spring-run Chinook salmon in Butte Creek had extremely low spawning runs in 2023 and 2024 (Figure 1).
In part, this was because all Sacramento River Valley salmon populations are collapsing due to the direct and indirect effects of the 2020-2022 drought and related management actions, on top of climate change and catastrophic fires.1 Drought conditions in 2021 and 2022 in the spawning rivers, lower Sacramento River, Delta, Bay, and ocean all contributed to poor juvenile salmon survival.
The poor number of Butte Creek spawners in 2024 is also related to the high pre-spawn mortality of adult salmon in Butte Creek in 2021,2 as a result of drought conditions during the winter-spring upstream migration and summer-fall holding and spawning.
Despite the failures of brood years 2020 and 2021, there is optimism for brood year 2022 and its spawning run in 2025 (Figure 2). Water year 2023 was a wet year, with good young survival conditions for juvenile salmon. Though brood year 2022 had only about 3700 spawners, , the returning adults were able to migrate and spawn with minimal stress in a drought year.
The uncertainty that remains is the survival of brood years 2023 and 2024, because of their potential small number of returning spawners in 2026 and 2027. Water year 2024 was a above-normal water year, but it was not without its stresses.3 Early indicators suggest 2025 could be a dry year. The potential for small runs to lead to strong brood years also leaves room for doubt given that four recent years of poor spawners led to poor recruitment (four dots at lower left in Figure 2).
The poor spawner numbers in 2023 and 2024, coupled with the uncertain forecasts for runs in 2025-2027, represent a serious population threat that calls for strong actions to save the species and rebuilding the spawning stock.
Winter Actions
Winter fry-fingerling emigration down lower Butte Creek past the Parrot-Phelan Diversion Dam and the primary screw trap counting station occurs in earnest beginning in mid-December, with a peak in January. The peak in fry emigration (the main element of juvenile salmon production from Butte Creek) occurs during early winter precipitation events. The fry, often still feeding on their yolk sac, leave the cold turbid creek heading for warmer, low-velocity food-rich floodplain waters of the Butte Basin and the Sutter Bypass, and for the tidewater of the Bay-Delta.
Strong winter growth is essential for good survival (good growth rates, and lower rates of starvation and predation). Strong winter growth promotes early smoltification and entry to the ocean. The main success factors in winter are adequate transport flow, access to and from floodplain habitats in the Butte Basin and Sutter Bypass, and low predation rates.
Spring Actions
Pre-smolt, sub-yearling smolts, and yearling smolts emigrate in modest numbers from Butte Creek in spring. These late migrants contribute to population numbers and genetic diversity. Success of these late migrants depends on high transport rates, low water temperatures, minimal diversion to often excessively warm floodplain habitats, minimal entrainment into unscreened water diversions, and minimum flow-through rates from river to floodplain habitats.
Adult spring-run salmon migrate from the Bay to upper Butte Creek in spring. They require adequate flows and water temperatures often not available in drought years, especially in late spring.
Specific Winter and Spring Actions to Consider:
Minimize water diversions at Parrot-Phelan Diversion Dam (and other creek diversions). In early winter, prioritize flow in Butte Creek over diversions for waterfowl pond flood-up and rice field decomposition (Figure 3), except in high runoff conditions. In spring, maintain flow in Butte Creek at the highest levels possible for attraction and holding except in early spring flood conditions.
Minimize the flow split into Sanborn Slough at bifurcation weir. Do not force more than 30% of Butte Creek flow into Sanborn Slough, which reduces important benefits of floodplain access and inundation.
Minimize diversions in Butte Basin and Sutter Bypass.
Keep Butte Slough Outfall closed except under Butte Creek flood relief conditions; instead, maximize flow through Butte Basin and Sutter Bypass.
In the event of dry-drought conditions, capture juvenile salmon at screw trap locations and Parrot Phelan Screen Bypass, and transport them to the mouth of Butte Creek, Verona, a conservation hatchery, downstream floodplain habitat, or a Bay-Delta location.
Maintain adequate transport flows in the lower Yolo Bypass and lower Sacramento River, and into and out of the Delta in winter, to maximize survival to the Bay and ocean.
Figure 1. Butte Creek spring-run salmon population (escapement or spawning run size) from 1975 to 2024. Red circle highlights dramatic decline in 2023 and 2024.Figure 2. Spawner/recruit relationship for Butte Creek spring-run salmon with three-year lag between spawners and recruits. Numbers shown in chart are return years (recruits). Blue is a wet year two years prior to spawning run when salmon were rearing and migrating to the ocean. Green are normal water years. Red are dry and critically dry years. Year labeled 25 is expected return run in 2025. Purple line is potential range of runs in 2026 and 2027 depending on success of brood years 2023 and 2024.Figure 3. Water diversion rate at Parrot-Phelan Diversion Dam fall 2023 to fall 2024 (water year 2024).
