Summer Report

This report shows trends in water quality, plankton, and fish across multiple IEP surveys for June through August from 1966 to 2022.


Delta Outflow

  • Freshwater flow influences water quality, plankton, and fish populations.
  • Summer flow is driven primarily by upstream dam releases and exports.
  • In 2022, net Delta outflow was lower than the long-term average.
mean is represented by a dotted red line

Figure 48: mean is represented by a dotted red line

Graph of net Delta outflow from 1966 to 2022. Values range from 2.6 to 46.1.

Figure 49: Graph of net Delta outflow from 1966 to 2022. Values range from 2.6 to 46.1.


Secchi Depth

Background

  • Organisms in this ecosystem are adapted to high turbidity conditions, and reductions in turbidity can have many negative ecological effects.
  • Higher values for Secchi depth indicate lower turbidity.
  • Secchi depth is measured monthly by DWR’s Environmental Monitoring Program by dropping a black-and-white disk in the water until it disappears.
image of a secchi disk

Figure 50: image of a secchi disk

Average Secchi Depth by Region

mean is represented by a dotted red line

Figure 51: mean is represented by a dotted red line

missing data are represented by tan triangles

Figure 52: missing data are represented by tan triangles

San Pablo Bay

 

Suisun

 

Delta
Graph of average summer secchi depth in San Pablo from 1976 to 2022. Values range from 33.8 to 228.2.

Figure 53: Graph of average summer secchi depth in San Pablo from 1976 to 2022. Values range from 33.8 to 228.2.

 

Graph of average summer secchi depth in Suisun from 1975 to 2022. Values range from 23.2 to 70.5.

Figure 54: Graph of average summer secchi depth in Suisun from 1975 to 2022. Values range from 23.2 to 70.5.

 

Graph of average summer secchi depth in Delta from 1975 to 2022. Values range from 32.7 to 135.2.

Figure 55: Graph of average summer secchi depth in Delta from 1975 to 2022. Values range from 32.7 to 135.2.

In 2022, San Pablo secchi depth was lower than the long-term average.

 

In 2022, Suisun secchi depth was close to the long-term average.

 

In 2022, Delta secchi depth was higher than the long-term average.

For more information see: Schoellhamer, D. H. 2011. Sudden clearing of estuarine waters upon crossing the threshold from transport to supply regulation of sediment transport as an erodible sediment pool is depleted: San Francisco Bay, 1999. Estuaries and Coasts 34(5):885-899. https://link.springer.com/article/10.1007/s12237-011-9382-x


Water Temperature

Background

  • Water temperature is monitored monthly by DWR’s Environmental Monitoring Program.
  • High temperature can increase productivity and may trigger harmful algal blooms.
  • Increasing Summer temperatures may limit juvenile smelt survival.
  • Summer temperatures are lower closer to the ocean and slightly higher in the Delta.
picture of a thermometer in water

Figure 56: picture of a thermometer in water

Average Temperature by Region

mean is represented by a dotted red line

Figure 57: mean is represented by a dotted red line

missing data are represented by tan triangles

Figure 58: missing data are represented by tan triangles

San Pablo Bay

 

Suisun

 

Delta
Graph of average summer water temperature in San Pablo from 1976 to 2022. Values range from 18.2 to 20.8.

Figure 59: Graph of average summer water temperature in San Pablo from 1976 to 2022. Values range from 18.2 to 20.8.

 

Graph of average summer water temperature in Suisun from 1975 to 2022. Values range from 19.7 to 22.2.

Figure 60: Graph of average summer water temperature in Suisun from 1975 to 2022. Values range from 19.7 to 22.2.

 

Graph of average summer water temperature in Delta from 1975 to 2022. Values range from 20.8 to 23.9.

Figure 61: Graph of average summer water temperature in Delta from 1975 to 2022. Values range from 20.8 to 23.9.

In 2022, San Pablo water temperature was close to the long-term average.

 

In 2022, Suisun water temperature was close to the long-term average.

 

In 2022, Delta water temperature was close to the long-term average.

For more information see: Bashevkin, S. M., B. Mahardja, and L. R. Brown. 2022. Warming in the upper San Francisco Estuary: Patterns of water temperature change from 5 decades of data. Limnology & Oceanography. doi: https://doi.org/10.1002/lno.12057


Chlorophyll

Background

  • Chlorophyll is an indicator of phytoplankton production, which is low during the summer.
  • Phytoplankton are the base of the pelagic food web. It is sampled monthly by DWR’s Environmental Monitoring Program.
  • The invasion of the clam Potamocorbula amurensis caused a decline in phytoplankton and zooplankton after 1986 – especially in Suisun Bay.
picture of phytoplankton

Figure 62: picture of phytoplankton

Average Chlorophyll by Region

mean is represented by a dotted red line

Figure 63: mean is represented by a dotted red line

missing data are represented by tan triangles

Figure 64: missing data are represented by tan triangles

San Pablo Bay

 

Suisun

 

Delta
Graph of average summer chlorophyll in San Pablo from 1976 to 2022. Values range from 1.2 to 22.1.

Figure 65: Graph of average summer chlorophyll in San Pablo from 1976 to 2022. Values range from 1.2 to 22.1.

 

Graph of average summer chlorophyll in Suisun from 1975 to 2022. Values range from 1.2 to 28.4.

Figure 66: Graph of average summer chlorophyll in Suisun from 1975 to 2022. Values range from 1.2 to 28.4.

 

Graph of average summer chlorophyll in Delta from 1975 to 2022. Values range from 2.8 to 32.0.

Figure 67: Graph of average summer chlorophyll in Delta from 1975 to 2022. Values range from 2.8 to 32.0.

In 2022, San Pablo chlorophyll was higher than the long-term average.

 

In 2022, Suisun chlorophyll was lower than the long-term average.

 

In 2022, Delta chlorophyll was lower than the long-term average.

For more information see: Brown, T. 2021. 2019 Phytoplankton Annual Report. IEP Newsletter 40(2):47-52.


Zooplankton

Background

  • Zooplankton is sampled monthly by the CDFW/DWR Environmental Monitoring Program but sampling in San Pablo Bay did not begin until 1998.
  • Zooplankton are an important food source for pelagic fish.
  • Calanoid copepods and mysids are particularly good fish food. Cyclopoid copepods are not as good for fish food.
  • Biomass in summer tends to be the highest of the year, particularly for the calanoid copepod Pseudodiaptomous forbesi.
Copepod
picture of a copepod

Figure 68: picture of a copepod

Mysid
picture of a mysid

Figure 69: picture of a mysid

Average Zooplankton Biomass by Region

mean is represented by a dotted red line

Figure 70: mean is represented by a dotted red line

missing data are represented by tan triangles

Figure 71: missing data are represented by tan triangles

San Pablo Bay

 

Suisun

 

Delta
Graph of total summer zooplankton biomass in San Pablo from 1998 to 2021. Values range from 1.7 to 10.9.

Figure 72: Graph of total summer zooplankton biomass in San Pablo from 1998 to 2021. Values range from 1.7 to 10.9.

 

Graph of total summer zooplankton biomass in Suisun from 1975 to 2021. Values range from 5.2 to 44.7.

Figure 73: Graph of total summer zooplankton biomass in Suisun from 1975 to 2021. Values range from 5.2 to 44.7.

 

Graph of total summer zooplankton biomass in the Delta from 1975 to 2021. Values range from 5.5 to 40.6.

Figure 74: Graph of total summer zooplankton biomass in the Delta from 1975 to 2021. Values range from 5.5 to 40.6.

The long-term average is 6.3.

 

The long-term average is 15.2.

 

The long-term average is 16.0.

For more information see: Barros, A. 2021. Zooplankton Trends in the upper SFE 1974-2018. IEP Newsletter 40(1):5-14.


Fish

Background

  • Delta Smelt, listed as threatened by the Endangered Species Act, have been tracked by CDFW’s Townet Survey since 1959 in Suisun Bay, San Pablo Bay, and the Delta.
  • Northern Anchovy are an important forage fish in the brackish-saline regions of the estuary. They are sampled best by CDFW’s San Francisco Bay Study.
  • Sacramento Pikeminnow is a native cyprinid that is one of the few piscivorous native fish in the Delta. They are sampled by USFWS’s DJFMP beach seine surveys throughout the estuary.

Recent Trends

Background

  • Delta Smelt have been in severe decline over the past two decades, with a Summer Townet Survey index of zero in 2015, 2016, 2018, and 2019.
  • Microcystis is a toxic cyanobacteria first found in the Delta in 1998. Microcystis presence has been documented by the Environmental Monitoring Program and the CDFW Summer Townet Survey during their water quality sampling.
  • Aquatic vegetation in the Delta has increased significantly in recent years. This vegetation is composed mostly of non-native invasive plant species and is categorized as either floating or submerged types. Coverage is estimated by UC-Davis using remote sensing of the North and Central Delta.