Southern California agencies ramp up defenses as golden mussels breach State Water Project

Southern California agencies ramp up defenses as golden mussels breach State Water ProjectThe discovery of invasive mollusks in key conveyance infrastructure has prompted the Metropolitan Water District and Inland Empire Utilities Agency to deploy emergency chemical controls and launch long-term treatment studies.

Golden mussels have spread 400 miles from the Port of Stockton to Southern California since October 2024.

The Metropolitan Water District (MWD) appropriated $2 million for near-term mitigation equipment.

Unlike quagga mussels, golden mussels thrive in low-calcium waters, leaving most California reservoirs vulnerable.

MWD is leveraging 20 years of successful quagga containment in the Colorado River Aqueduct to inform its response.

IEUA is hiring consultant support to manage recharge operations using infested untreated water.

MWD and the Department of Water Resources are studying centralized control measures at Devil Canyon and Castaic Lake.

Water agencies in Southern California are mobilizing to protect critical infrastructure following the rapid spread of invasive golden mussels throughout the State Water Project (SWP). During a February 4, 2026, workshop, officials from the Inland Empire Utilities Agency (IEUA) and the Metropolitan Water District of Southern California (MWD) detailed the operational threat posed by the species, which was first discovered in the Port of Stockton in October 2024 and has since moved over 400 miles south. Dr. George DiGiovanni, Microbiology Unit Manager for MWD, reported that the mussels have been detected in Silverwood Lake, the Devil Canyon area, the Box Springs Feeder, and the Mills Plant Influent. Additionally, the Cucamonga Valley Water District recently identified adult mussels at connection CB 16. The mussels cluster on hard surfaces, threatening to clog intakes, small-diameter pipes, and valves. A key concern for operators is the species' adaptability. DiGiovanni noted that while quagga mussels require calcium concentrations of approximately 25 parts per million (ppm) to thrive, golden mussels can grow in water with calcium levels as low as 5 ppm. This makes most freshwater lakes and reservoirs in California vulnerable to infestation, unlike previous biological threats that were limited by water chemistry. In response, MWD has appropriated $2 million for near-term mitigation actions, including $500,000 for equipment purchases. The district is deploying a mobile chlorinator to facilitate groundwater replenishment deliveries for the City of Burbank and is installing a chlorine injection system to protect the ozone cooling system at the Jensen Water Treatment Plant, which utilizes raw SWP water. This response builds on nearly two decades of experience managing invasive species. Since quagga mussels were detected in Lake Mead in 2007, MWD has successfully limited their spread in the Colorado River Aqueduct and protected Diamond Valley Lake through a regimen of continuous chlorination, annual desiccation shutdowns, and diver-led cleaning. Officials aim to adapt these containment successes to the State Water Project, despite the golden mussel's broader environmental tolerance. Longer-term strategies involve a joint feasibility study between MWD and the Department of Water Resources (DWR) to install centralized control measures at the Devil Canyon and Castaic Lake outlets. DiGiovanni indicated that chloramination is a likely solution for permanent system design to avoid elevating trihalomethanes (THMs) in the water supply, noting that copper-based treatments pose challenges regarding discharge permitting and sensitive species. IEUA, which receives untreated SWP water, is also taking direct action. Michael Hurley, an IEUA staff member, confirmed that the agency is bringing on consultant support to address the complexities of using mussel-infested water for groundwater recharge. Operations and Maintenance Manager Mickey Chaudhary of MWD emphasized that eradication is unlikely, stating that the goal is effective management through a multi-barrier approach involving chemical and physical controls.