Category Archives: Water Quality

American River Salmon Update – Spawning Season, November 2025

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In a 10/19/2023 post and a 11/21/2024 post, I discussed how the lack of access to Folsom Reservoir’s deep cold-water pool results in delayed natural and hatchery spawning of American River fall-run salmon.  Delays, and spawning in warmer water, cause reductions in spawning success, smolt production, recruitment into harvestable fishery stocks, and spawning escapement (run size) to the American River.  Lower salmon contributions from the American River significantly reduce California coastal and river salmon fishery stocks.  Poor production in the American River contributed to the closure of California salmon fisheries in 2023-2025.

During the 2020-2022 drought, Reclamation released water from the lower-level power bypass (sacrificing hydropower production) to provide the cold water (<55ºF) salmon needed for spawning in the ten-mile spawning reach from Nimbus Dam (near Fair Oaks gage) to the William Pond gage (Figure 1).  This is the prime spawning reach for salmon in the lower American River.  However, in the fall of the wetter years 2023-2025, Reclamation did not use the power bypass to release cold water (Figures 2 and 3), despite higher storage levels than during the drought (Figure 4).  The lack of cold water delayed natural spawning and hatchery egg taking, to the detriment of egg viability, fry production, and smolts reaching the ocean.

Ultimately, the number of adult salmon returning to the American River to spawn (escapement) is the important measure of success.  There are many factors that may contribute to the number of returns.  Recent returns are up (Figure 5).  The 2023 and 2024 returns were good despite having been the product of the 2020-2022 drought reproduction (Figurer 6).  Closed fisheries in 2023 and 2024 contributed to higher escapements.

I also believe efforts to improve fall water temperatures below Folsom during the drought improved both the wild and hatchery components of escapement.  I remain concerned that a return to warmer fall water temperatures will hinder future escapement.

I am also concerned with apparent efforts to sustain higher fall 2025 reservoir levels (see Figure 4) by reducing tailwater stream flow rates (Figure 7).  Such low flows reduce the quantity and quality of salmon spawning habitat.  Many critical spawning side channels become dewatered at such low flows1.  Main channel velocities, substrate, and depths are also compromised at low flow rates.

Reclamation  also reduced funding for the salmon hatchery and for river habitat projects in 2025, and will likely do the same in subsequent years.  This strategy will not help to recover American River salmon stocks to levels that once again can contribute toward commercial and recreational salmon fisheries.

Figure 1. Map of three CDEC gaging stations on the lower American River.

Figure 2. Average daily water temperatures in Nov-Dec period at William Pond gage 2021-2025. Red line (55ºF) denotes upper safe level for Chinook spawning.

Figure 3. Average daily water temperatures in November period at Fair Oaks gage 2021-2025. Red line (55ºF) denotes upper safe level for Chinook spawning.

Figure 4. Late summer and fall Folsom Reservoir water storage (acre-feet) 2021-2025.

Figure 5. Adult salmon escapement estimates for the American River 1975-2024. Source: Grand Tab.

Figure 6. American River spawner/recruit relationship – { log10(escapement) -3.5]. Number is year of escapement (recruits). Color denotes water year type two years prior. Red is dry, green is normal, and blue is wet. Note escapement in 2023 and 2024 are red, denoting spawning and rearing occurred two years earlier in dry water years.

Figure 7. Streamflow (daily average) in the American River at Fair Oaks gage Aug-Nov period 2021-2025.

Reclamation plans to take more water from the Delta

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A December 3, 2025 article in the LA Times warns of the federal government’s plan to take more water from the Delta. This is not something new – they have maximized exports much of this year and last year (Figure 1).  The State of California has also been doing this, but to a lesser extent (Figure 2).  Together, the two projects can export up to 22,000 acre-ft per day (8,000 acre-ft/day at Tracy, 14,000 acre-ft/day at Banks).  In a wet (2023) or above-normal year (2024 and 2025) exports can exceed 6-million acre-feet out of a potential maximum export pumping capacity of 8 million acre-feet.

The projects were able to exceed expectations in above-normal water year 2025 by eliminating the Fall-X2 Action that over the past decade required higher Delta outflows and lower exports in the September-October period to protect Delta smelt in the Bay-Delta.  In September 2025, the projects were able to export 674,000 acre-feet by dropping the Fall-X2 Action, compared to 536,000 acre-feet in September 2024 when the Fall-X2 Action was implemented.

The increased September exports in 2025 had significant environment effects that impacted salmon, smelt, and other Bay-Delta native fishes.

  • First, Delta outflow to the Bay was reduced in half (about 300,000 acre-feet, Figure 3) through a combination of the higher exports and lower reservoir releases (Delta inflow, Figure 4). That led to higher temperatures of water entering the Bay and the low salinity zone (LSZ) moving upstream from the Bay into the west Delta channel near Rio Vista (Figures 5 and 6).  These effects are detrimental to salmon at the peak of their fall migration into the Bay from the ocean and to the low salinity zone, which is designated critical habitat for smelt.
  • Second, lower Delta inflow from the Sacramento River (Figure 4) led to higher water temperatures in the north Delta at Rio Vista (Figure 6) and Freeport (Figure 7).
  • Third, reduced flows in the lower Sacramento River (Wilkins Slough, Figure 8) led to higher water temperatures (Figure 9), detrimental to salmon during their spawning migration to the upper Sacramento River and its tributaries.

In drier years (below-normal, dry, and critical), there are no Fall-X2 Actions, but there are many other restrictions on river flows, exports, and reservoir storage use to protect fish and their habitat as well as future water supplies.  In the past, Delta exports in drier years have been limited to only 3 to 5 million acre-feet per year.  We have yet to see the federal government’s plan to export more water in such years.  We can only guess as to what drastic changes to expect and the environmental damage that could ensue with the new federal export plan.  Higher spring exports in 2025 (see Figure 1) is one such change.

Figure 1. Federal exports from the south Delta via the Tracy Pumping Plant (TRP) in 2024 and 2025

Figure 2. State exports from the south Delta via the Harvey Banks Pumping Plant (HRO) in 2024 and 2025.

Figure 3. Delta Outflow to the Bay in Aug-Sept period of 2024 and 2025. The Fall-X2 Action was not implemented in September 2025.

Figure 4. Streamflow in the north Delta at the Freeport gage May-Dec 2024 and 2025. The Fall-X2 Action was implemented in September 2024 but not in September 2025 nor in October 2024 or 2025.

Figure 5. Salinity and water temperature in the west Delta near Rio Vista from August 2023 through September 2025 with emphasis on Sep-Oct period. Red lines denote water temperature (20C) above which there is significant stress on migrating adult fall-run salmon. The Fall-X2 Action was not implemented in October 2024 or September 2025.

Figure 6. Water temperature in the Sacramento River channel at the Rio Vista Bridge gage Aug-Sep 2024 and 2025. The Fall-X2 Action was not implemented in September 2025.

Figure 7. Water temperature in the Sacramento River channel at the Freeport gage in September 2024 and 2025. The Fall-X2 Action was not implemented in September 2025.

Figure 8. Streamflow in the lower Sacramento River at the Wilkins Slough gage in September of 2024 and 2025. The Fall-X2 Action was not implemented in September 2025.

Figure 9. Water temperature in the lower Sacramento River at the Wilkins Slough gage in September of 2024 and 2025. The Fall-X2 Action was not implemented in September 2025.

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

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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

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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

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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?

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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.

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

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

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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