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Environmental Characteristics of Select Managed Ponds in the Sacramento–San Joaquin Delta: Implications for Native Fish Conservation and Research

Open-File Report 2025-1040
Prepared in cooperation with Metropolitan Water District and State Water Contractors
By: , , , , , , and 
https://doi.org/10.3133/ofr20251040

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Abstract

The use of wetlands to support native fish research and conservation efforts in the Sacramento–San Joaquin Delta (Delta) of California is a growing priority. The purpose of our study was to examine the physiochemical and biological characteristics of select managed ponds in the Delta to determine if they would be suitable habitats for research involving the conservation of delta smelt (Hypomesus transpacificus). We studied 10 managed ponds distributed across the central part of the Delta situated on Bacon Island and Bouldin Island in San Joaquin County, and Holland Tract and Webb Tract islands in Contra Costa County. The managed ponds had a diversity of physical habitat configurations and were not directly connected to waterways surrounding the islands and, therefore, not affected by tides. We studied the managed ponds from approximately November 2021 to December 2023 to assess water quality, zooplankton, fish, and pesticide metrics. Water levels in the managed ponds were managed to varying degrees and were mostly independent of climate-driven wet-dry seasonality. Water quality conditions varied among ponds and were independent of geographic location. Overall, mean monthly chlorophyll a concentration ranged from 15 to 57 (mean=30) micrograms per liter (μg/L), dissolved oxygen concentration ranged from 4 to 9 (mean=7) milligrams per liter (mg/L), pH was 8, salinity was 1 practical salinity units (PSU), specific conductance ranged from 1,202 to 1,839 (mean=1,471) microsiemens per centimeter (μS/cm), and turbidity ranged from 13 to 24 (mean=19) Formazin Nephelometric Units (FNU). Water temperature thresholds that contribute to stress (21 degrees Celsius [°C]) and mortality (28 °C) of delta smelt were often exceeded during summer and fall, though vertical stratification contributed to lower bottom temperatures in the deepest managed ponds, which could potentially provide thermal refugia for delta smelt so long as dissolved oxygen concentrations are suitable. Zooplankton populations were broadly similar among managed ponds and included calanoid and cyclopoid copepods that would be suitable prey for delta smelt. Overall average total zooplankton biomass, as measured with a Schindler-Patalas trap, was 0.6 μg/L (min=0, max=63.6) and peaked during spring at more than 4 μg/L. Fish populations highly varied among the managed ponds with potential predators of delta smelt such as largemouth bass (Micropterus salmoides) and black crappie (Pomoxis nigromaculatus) present in several of the managed ponds; predator distribution among ponds seemed to have been driven primarily by deliberate stocking to facilitate local fisheries. Measured pesticide concentrations were below U.S. Environmental Protection Agency Aquatic Life Benchmarks except for exceedances of three compounds (diuron [herbicide], clothianidin [insecticide], and deltamethrin [pyrethroid insecticide]) in samples collected from ponds on Bouldin Island and Webb Tract. Overall, most managed ponds seemed suitable to support delta smelt, though physical control of potential predators and summer temperature might be needed. The results provide guidance on how to engineer and manage new managed ponds to support research and conservation efforts for delta smelt and other native fishes.

Suggested Citation

Feyrer, F.V., Acuña, S., Buxton, J.M., Enos, E.R., Hladik, M.L., Orlando, J., and Young, M.J., 2025, Environmental characteristics of select managed ponds in the Sacramento–San Joaquin Delta—Implications for native fish conservation and research: U.S. Geological Survey Open-File Report 2025–1040, 35 p., https://doi.org/10.3133/ofr20251040.

ISSN: 2331-1258 (online)

Study Area

Table of Contents

  • Acknowledgements
  • Abstract
  • Introduction
  • Study Area
  • Methods
  • Results
  • Discussion
  • References Cited
  • Appendixes 1–3
Publication type Report
Publication Subtype USGS Numbered Series
Title Environmental characteristics of select managed ponds in the Sacramento–San Joaquin Delta—Implications for native fish conservation and research
Series title Open-File Report
Series number 2025-1040
DOI 10.3133/ofr20251040
Publication Date July 23, 2025
Year Published 2025
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) California Water Science Center
Description Report: viii, 35 p.; Data Release
Country United States
State California
County Contra Costa County, San Joaquin County
Other Geospatial Bacon Island, Bouldin Island, Holland Tract Island, Webb Tract Island
Online Only (Y/N) Y
Additional publication details