Category Archives: Water Quality

The 2025 Sacramento River Salmon Run – Early Summer Conditions were poor

Posted on by

The limited 2025 salmon fishing season opened in mid-July and continues through October on the Feather, American, and Mokelumne rivers.  Early summer (July-August) conditions were tough for the beginning of the run and early fishing.  The river, Delta, and Bay in August were too warm despite three wet years in a row with above average reservoir storage and below normal summer air temperatures.

The lower Sacramento River was too warm (Figure 1). Flows dropped in mid-August with two-thirds of reservoir releases being diverted before reaching the Delta.  Water temperatures were above the 20ºC standard to protect salmon during their run from the ocean to the rivers.  River flow should be near 10,000 cfs to maintain the water temperature standard.

The Delta was too warm (Figure 2).  Water temperatures in August reached the 22ºC level, considered highly stressful and avoided by salmon, as Delta inflow dropped from 20,000 cfs to 10,000 cfs.  Delta inflow at Freeport should be about 20,000 cfs for good fishing conditions.

The Bay was too warm (Figure 3).  Water temperatures exceeded 22ºC, and dissolved oxygen fell to near the standard of 6 mg/ l.  Delta outflow fell to near 4000 cfs, while south Delta exports exceeded 10,000 cfs.  Delta outflow should be around 10,000 cfs for good fishing conditions.

Figure 1. Lower Sacramento River streamflow and water temperature in July-August 2025. Red line is the water quality standard for water temperature.

Figure 1. Lower Sacramento River streamflow and water temperature in July-August 2025. Red line is the water quality standard for water temperature.

Figure 2. Streamflow and water temperature of the Sacramento River at northern entrance to the Delta over the past 30 days.

Figure 3. Water temperature and dissolved oxygen concentration in the east Bay in July-August 2025.

The Fall-X2 Action – Benefits and Costs

Posted on by

The 2008 Delta Smelt Biological Opinion for Central Valley Project (CVP) and State Water Project (SWP) operations included the Fall X2 Action to protect Delta smelt. The about-to-be implemented “Action 5” that will modify the 2024 biological opinions for the CVP and SWP will eliminate the Fall X2 Action entirely.

The Fall X2 Action required the CVP and SWP to keep brackish water west of the Delta in September and October in wet and above normal water years. The X2 location is defined as the location where salinity is 2 parts per thousand.1 X2 is located within what is known as the low salinity zone (LSZ, 1-6 parts per thousand).

Delta smelt and longfin smelt concentrate in the LSZ near X2 in summer and fall. Keeping X2 at Chipps Island (KM 71 from the Golden Gate, Figure 1) benefits the populations of Delta smelt and longfin smelt. Less effective options for the Fall X2 Action that require less Delta outflow have included other locations as far east as KM 80.

If freshwater outflow from the Delta is too low (at or below about 6000 cfs), the LSZ is located within the narrow channels of the west Delta. Water in the west Delta tends to be warmer and less productive than water in Suisun Bay. It is also more likely to be pulled south by pumping at the CVP and SWP’s south Delta export facilities.
The higher freshwater inflows needed for the Fall X2 Action also benefit other native fishes in the lower Sacramento River, its tributaries, and the Delta.

Harm comes to Bay-Delta fish in the form of high water temperatures and reduced food concentrations. When water temperatures climb into the range of 70-72°F, native fishes, including smelt, sturgeon, steelhead, and salmon, generally suffer stress-related poor growth and survival.

Warm Delta water blocks or hinders adult salmon in their upstream spawning migrations. (A water temperature of 72°F is the salmon avoidance temperature.) Adult salmon will hold in the Bay because of warm water temperatures, resulting in delayed spawning and the expenditure of the critical energy needed for spawning. Warm rivers cause further delay, diseases, and thiamine deficiency, reducing the ability of salmon to spawn successfully. Higher water temperatures (> 65°F) during spawning migrations also lead to reduced salmon egg and embryo survival. High water temperatures in juvenile rearing habitat and emigration routes lower the growth and survival of juvenile salmon, steelhead, smelt, and sturgeon, and increase predation on all these species.
In the Delta specifically, high water temperatures in the Delta block emigration of juvenile salmon and reduce growth rates and survival of juvenile salmon and smelt. Both salmon and smelt species are highly sensitive to warm and varying water temperatures. Heat transfer and retention during high air temperatures from late-spring to early-fall is greater at lower flows.

In summary, water temperatures above 72°F are highly stressful on native Bay-Delta fishes, often leading to poor growth, low-oxygen stress, more disease, greater susceptibility to predation, and competition from non-native fish, all of which lead to reduced survival. Also, many non-native fish such as largemouth bass thrive in higher water temperatures (72- 80°F).

The Fall X2 Action
The Fall X2 Action focuses on increasing Delta inflow and outflow in the months of September and October when seasonal flows are naturally lower and irrigation demands less, while air temperatures remain high. Late summer and early fall are a key period in the life cycle and overall reproductive success of many Bay-Delta native fishes.

Bay-Delta
The Fall X2 Action is needed to maintain low salinity and water temperature in the optimal range of native Bay-Delta fish. In the 2017-2019 period, with two wet years and one below-normal year, the higher prescribed Delta outflow (DTO) of the Fall X2 Action (Figure 2) in the wet years kept the Bay fresher (Figure 3) and Delta outflows cooler (Figures 4 and 5). In the two above-normal years of 2024 and 2025, the lack of a Fall X2 Action in September 2025 (Figure 6) led to high September water temperatures in the western Delta (Figure 7). The lack of Fall X2 Action in October 2024 (Figure 6) contributed to stressful (>65º F) October water temperatures at Rio Vista bridge in the west Delta (Figure 7). 2020, a below normal water year, provides another example of high September-October water temperatures when the Fall X2 Action was not implemented (Figure 8).

Lower Rivers
The Fall X2 Action requires roughly 5000 cfs of extra Delta inflow for two months (assuming needed flow is not provided by foregone river diversions or Delta exports). Releases from Shasta, Oroville, and/or Folsom reservoirs generally provide this inflow. That amounts to roughly 10,000 acre-feet of water per day, or 600,000 acre-feet for the full September-October period. In recent wetter water years, the CVP and SWP have offset some (or all) of this water cost by reducing reservoir releases in the summer and not meeting water quality standards for water temperatures in the lower Sacramento River. Flows in the lower Sacramento River at Wilkins Slough have been near 5000 cfs, when it takes about 10,000 cfs to maintain the 68º F standard.

The Cost
In summary, the amount of fresh water required to keep X2 in Suisun Bay in late summer and early fall of above-normal and wet water years requires approximately 600,000 acre-feet of stored project water or forgone diversions from rivers and exports from the Delta. That amounts to about 5% of total CVP and SWP storage capacity. It is also about 5% of the total annual upstream, in-Delta, and Delta export water use in the Bay-Delta watershed.

The about-to-be implemented “Action 5” that will modify the 2024 biological opinions for the CVP and SWP will eliminate the Fall X2 Action, and this water cost, entirely.

Figure 1. Bay-Delta and key water accounting and water quality locations.

Figure 2. Daily average Delta outflow (cfs) in September-October of water years 2017-2019. Fall X2 Action was implemented in wet year 2017 and 2019.

Figure 3. Salinity (EC) of east Bay near Chipps Island at Mallard Slough 2017-2019.

Figure 4. Water temperature in west Delta at Emmaton in September-October 2017-2019.

Figure 5. Water temperature in west Delta at Rio Vista in September-October 2017-2019.

Figure 6. Daily average Delta outflow (cfs) in September-October of above-normal water years 2024 and 2025. Fall X2 Action was implemented in September of 2024 and October of 2025.

Figure 7. Water temperature in west Delta at Emmaton and Rio Vista in September-October 2024 and 2025.

Figure 8. Daily average Delta outflow (cfs), Freeport river flow, and Emmaton and Rio Vista water temperature in July-October of water year 2020. The Fall X2 Action was not implemented in below-normal water year 2020.

  1. Also measured as about 3000 EC.  See https://pubs.usgs.gov/sir/2014/5041/pdf/sir2014-5041.pdf ↩

2025 Sturgeon Moon

Posted on by

The 2025 Sturgeon Moon (August 9 full moon) wreaked havoc on San Francisco Bay as it had in recent years1. The main effect was warm fresh water from the Delta draining into the Bay (Figure 1). The tidal effect of the super moon dropped water levels sharply about two weeks before the super moon (Figure 2). Warm water built up in the Bay over several days (Figure 3). A plankton bloom appeared in the North Bay soon thereafter (Figure 4). Is anyone checking on the sturgeon in the Bay? Will the coming heat waves over-heat the Bay?

Chart

Figure 1. Fresh water drained into the Bay at Martinez for several days in late July, beginning about 14 days prior to the full moon.

arrow at chart

Figure 2. Water level of the Bay at Martinez July and early August 2025.

chart

Figure 3. Water temperatures increased at Martinez with the warm inputs from the Delta and Suisun Bay.

map

Figure 4. Small plankton blooms appeared around the peripheries of San Pablo and Suisun bays and in Montezuma Slough at the end of July with the warm freshwater inputs. Source: https://www.cbr.washington.edu/sacramento/data/query_river_graph.html

 

American River Salmon Update – Delayed Spawning, November 2024

Posted on by

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.

Figure 3. Folsom Reservoir storage levels 2015-2024.

Figure 4. Photo of closed-gate entrance to Nimbus Hatchery fish ladder 11/14/2024.

Summer 2024 Operations of the Shasta/Trinity Division of the CVP

Posted on by

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.

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.