USACE conducts dye testing in Sacramento River near Old Sacramento

The U.S. Army Corps of Engineers Sacramento District began conducting dye testing of the Old Sacramento floodwall along the Sacramento River on Oct. 29, 2025, as part of ongoing work to investigate the floodwall following high water levels in the Sacramento River in 2023.

After the water levels dropped, crews observed soil movement behind the floodwall. Despite this condition, the floodwall remains safe. This investigation will help identify the most comprehensive approach to address this condition and maintain the long-term stability of the floodwall.

The dye testing is part of an initial investigation phase that also includes sampling and testing soils on both sides of the floodwall, measuring soil displacement behind the floodwall, and monitoring water levels in the river and in soil behind the floodwall. The comprehensive project is scheduled to occur from 2025 to 2028.

Crews are using fluorescent yellow/green water tracing dye to assess water movement between the river and soil behind the floodwall. This type of testing is commonly used in major infrastructure projects for leak tracing, overflow analysis, discharge testing and dispersion pattern analysis.

Residents and boaters may observe bright yellow/green coloration in the river water during testing periods that began Oct. 29, 2025, and could potentially extend into spring 2026, depending on water levels. Signs have been posted to inform the public about the dye testing. The dye being used is non-toxic and biodegradable. Depending on soil conditions and water flow, extended time may be required to observe the dye, ranging from as little as seconds to possibly weeks.

The floodwall testing falls under USACE's Public Law 84-99 Rehabilitation Program, in coordination with the City of Sacramento and the Central Valley Flood Protection Board. PL 84-99 authorizes USACE to assist communities with flood preparedness and response, including rehabilitation of levees and floodwalls. Residents with questions about the testing can contact the Sacramento District Public Affairs Office at (916) 557-5100. For more information about the project, visit: https://www.spk.usace.army.mil/Missions/Emergency-Operations/PL-84-99/.

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