California Waters - Fall 2025 - Vol. V | Issue II
California’s water story is unlike any other. Our state’s diverse and dynamic hydrology presents unique challenges for water managers striving to meet the needs of communities, ecosystems, and industries—while also protecting people and places from water-related hazards. That’s why solutions based on innovative, thorough, and reliable science are so important. The research featured in this edition of California Waters highlights the kind of high-quality science that helps inform smart decisions across the state.
We’d love to hear from you:
- How are you using science from the USGS California Water Science Center?
- What water issues do you think we should study next?
- Are you interested in partnering with us to deliver the gold-standard science California—and the nation—needs?
Let’s work together to support a more resilient water future.
Anke Mueller-Solger, PhD
Center Director
California Water Science Center
Golden State Reflections
Sentinel Site Modeling
The California Department of Fish and Wildlife (CDFW) installed more than 40 climate and biodiversity monitoring stations, called sentinel sites, on public lands across the state. These sites collect detailed data on things like temperature, precipitation, soil moisture, and more to track how the environment is changing. Each site is meant to reflect conditions in the surrounding area, but...
An integrated sensor network and data driven approach to satellite remote sensing of dissolved organic matter
Traditional remote sensing retrieval models for water quality have historically relied on limited, localized data sets due to the prohibitive costs of extensive field campaigns and logistical challenges of collecting match-up data with satellite overpasses. As a result, these models often lack generalizability across seasons, tides, and sites. Furthermore, small field data sets limit the...
USGS Water Science Centers Partner at 2025 Lake Tahoe Summit
Scientists from the California and Nevada Water Science Centers attended the 29th annual Lake Tahoe Summit to discuss the work the USGS is doing in the Tahoe Basin. This year’s event honored the legacy of U.S. Senator Dianne Feinstein and her commitment to Lake Tahoe.
Central Valley Hydrologic Model - Version 2
A new tool for evaluating water management in California's Central Valley
2022 McKinney rain-on-wildfire event, dissolved oxygen sags, and a fish kill on the Klamath River, California
The longitudinal propagation of water-quality and ecological impairments in rivers during and after wildfires remain poorly understood. In Northern California, the 2022 McKinney Fire burned 243 km2 of the Klamath National Forest, with 83% of the burned area classified as moderate to high severity. During the active wildfire, a high-intensity monsoonal rain event triggered sediment-laden...
Identifying organic contaminants at trespass cannabis grows on federal land in California, USA
Despite the legalization of recreational cannabis in California, USA, illegal cannabis cultivation remains pervasive, partly through the establishment of illegal cultivation on public lands (trespass grows). These operations often illegally divert water for irrigation and perform unauthorized applications of chemical fertilizers and pesticides. This work investigates a broad suite of...
Select Borehole Data for the Salton Sea area and vicinity, Imperial-Riverside-San Diego-San Bernardino Counties, CA
Borehole lithology data from drillers' log descriptions were compiled for the Salton Sea area and vicinity. This data will be utilized to support hydrogeologic and hydrologic investigations. Data for some parts of the Salton Sea Watershed were already compiled for other USGS reports. These included Borrego Valley (Faunt and others, 2015), and the East Mesa (Shepherd and Rosenberg, 2024)...
Bioenergy and Pesticides: Lessons from the AltEn Bioenergy Plant
Ethanol production from seed corn, while reducing waste and promoting renewable energy, can have environmental and health implications. A USGS study on a former bioenergy plant that received pesticide-coated seeds used for ethanol production, revealed that the process led to contaminated wastewater and solid residue, resulting in elevated pesticide levels in nearby surface waters even after the...
Quality of groundwater used for domestic supply in the Gilroy-Hollister basin and surrounding areas, California, 2022
More than 2 million Californians rely on groundwater from domestic wells for drinking-water supply. This report summarizes a 2022 California Groundwater Ambient Monitoring and Assessment Priority Basin Project (GAMA-PBP) water-quality survey of 33 domestic and small-system drinking-water supply wells in the Gilroy-Hollister Valley groundwater basin and the surrounding areas, where more...
Pyrethroid insecticides implicated in mass mortality of monarch butterflies at an overwintering site in California
Since the 1980s, monarch butterfly (Danaus plexippus plexippus) populations across North America have declined by 80–95%. Although several studies have implicated pesticides as a contributing factor to their population declines, our understanding of monarch exposure levels in nature remains limited. In January 2024, a mass mortality event near an overwintering site in Pacific Grove...
Environmental characteristics of select managed ponds in the Sacramento–San Joaquin Delta—Implications for native fish conservation and research
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...
Assessing spatial variability of nutrients, phytoplankton, and related water-quality constituents in the California Sacramento–San Joaquin Delta at the landscape scale—Comparison of four (2018, 2020, 2021, 2022) spring high-resolution mapping surveys
Executive SummaryThis report summarizes results from boat-based, high-resolution water-quality mapping surveys completed before, during, and after upgrades to the EchoWater Resource Recovery Facility (EchoWater Facility), the regional wastewater facility for the City of Sacramento and surrounding areas, near Elk Grove, California. Surveys were completed in the tidal aquatic environments...
Public supply water delivery analysis and estimation for the conterminous United States
Public supply water withdrawals represent 14% of all withdrawals in the conterminous United States (CONUS), supplying approximately 87% of the population with fresh water. Deliveries for public water supply are crucial for associating water use amounts with populations because they often differ from total withdrawals due to wholesales, transfers, losses, and other factors. Understanding...