Golden mussels, an invasive mollusk, pose a significant threat to natural ecosystems and water infrastructure due to their ability to form dense colonies. First identified in the Delta in October 2024, these invasive mussels are highly adaptable, tolerating a wide range of environmental conditions, including varying salinity levels. Once established, golden mussels can disrupt ecosystems by outcompeting native species for food, altering water quality and biofouling surfaces, leading to costly damage to water systems and infrastructure.
Recognizing the urgent need for coordinated action, a dedicated task force was formed in late October 2024. This group brought together eight key agencies, including the Department of Fish and Wildlife, the Division of Boating and Waterways, and the US Fish and Wildlife Service, among others, all of which have authority or are directly impacted by the presence of golden mussels. By April 2025, the task force released a comprehensive response framework outlining strategies to address this issue. Martha Volkoff, Program Manager with the California Department of Fish and Wildlife, provided an overview of the framework at the May meeting of the Delta Independent Science Board.
The primary objective of the framework and task force is to prevent the further spread of golden mussels and reduce their negative impacts on the environment, economy, infrastructure, and public health. The framework outlines activities aligned with established invasive species management practices, emphasizing communication and public engagement of users and potential vectors. These vectors include activities that may unintentionally spread golden mussels, such as water movement and overland transport through boating, which provide strategic opportunities, such as boat inspections, to intervene and limit the spread of golden mussels.
Ms. Volkoff noted that the Department of Fish and Wildlife operates an established quagga and zebra mussel program with dedicated staff and resources focused on these two species. Under the Fish and Game Code, DFW’s authority explicitly pertains to dreissenid mussels, including quagga and zebra mussels. Since the golden mussel belongs to a different genus, its management does not fall under the same authority. However, because the strategies for managing and preventing the spread of golden mussels are similarly aligned, DFW is integrating related activities into its existing staff and resources. That said, there are critical gaps in authority for addressing golden mussels, which DFW is actively working to resolve.
FRAMEWORK OBJECTIVES:
The framework is a document of recommendations, some of which are being implemented and some of which require authority or funding to be implemented. There are seven objectives:
Communication
There are two components: media and outreach. Media communication focuses on creating and coordinating a unified media plan across agencies to ensure consistency when interacting with media outlets. On the other hand, outreach aims to educate and inform the general public. Staff from multiple agencies are actively involved in developing the outreach plan.
“Our experiences over working on quagga and zebra mussels is the goal of tailoring outreach material to specific audiences because we feel it reaches and resonates more strongly when potential vectors associate this issue with their particular activity,” said Ms. Volkoff. “So we’re working on developing materials, distribution channels, and a social media presence.”
Containment
The goal is to prevent the overland transport of infested watercraft and equipment. Currently, the Delta is the primary infested area, presenting significant challenges due to its numerous access points, many of which lack strong regulations. There are also private access points that are managed independently.
“This is one of the objectives where funding and authority are challenging for implementation of effective containment,” said Ms. Volkoff. “Currently there is no active containment being implemented in the Delta. We have been working on mapping out Delta launch sites, just so we can put our arms around if we did have the resources, what that footprint and implementation might look like.”
Efforts are also underway to develop signage that informs boaters they are in a mussel-infested zone and encourages them to follow clean-drain-dry practices when moving watercraft.
“In addition to outreach and education, that messaging of clean drain dry practice for all users in water every time you launch, whether you’re boating in a known infested water or not, is one of the underpinnings of our outreach and education and prevention messaging.”
Prevention at uninfested waters
The Department of Fish and Wildlife does not directly manage prevention programs at uninfested waters, as these fall under the jurisdiction of water managers or their concessionaires. However, DFW supports these efforts by providing staff to assist water managers in establishing watercraft inspection and decontamination programs.
Additionally, the task force is working to enhance statewide coordination of these programs by defining consistent standards, offering training and certification, and developing a network of service providers to assist water managers in effectively combating the spread of golden mussels.
“While we don’t have the authority to require any of these individual water managers to conform to any one program, what we can do is set up a standard and help coordinate across these programs to help leverage resources across different agencies to increase boater recreational access, while concurrently protecting their water body from the introduction of mussels.”
Monitoring
The Department has been working with agencies in the Delta to delineate the infestation and track the expansion and is conducting early detection monitoring at what are believed to be uninfested waters.
We have had detections throughout the state water project so we know that mussels and veligers and the mussel pop golden mussel population is expanding down through the state and federal water projects.
Partner engagement
The partner engagement team, which convenes bimonthly, serves as an inclusive platform for agencies, scientists, and policymakers to share updates, exchange ideas, and provide feedback on golden mussel management. This collaborative forum ensures that inputs from a wide range of stakeholders are gathered and relayed to the Golden Mussel Task Force for consideration.
Additionally, the team operates two specialized sub-teams of water managers. One sub-team focuses on prevention programs for uninfested waters, while the other concentrates on managing golden mussels in already infested areas, ensuring a comprehensive and targeted approach to addressing this invasive species.
Population suppression
Population suppression focuses on exploring and implementing strategies to reduce settlement, decrease reproductive success, and address biofouling. While this is a recognized objective within the framework, its implementation is currently beyond reach due to the need for additional funding, staffing, and resources. So, at a conceptual level, a foundation for population suppression has been established in the framework, but it remains a goal for future action.
Science and Capacity Building
The framework identifies key research priorities essential for their immediate management. Among these priorities are determining the lethal temperatures for golden mussel veligers and adults to guide prevention efforts, such as establishing effective dry times, implementing hot water decontamination protocols, and exploring chemical exposure methods for equipment cleaning.
A critical step in this research involves differentiating golden mussel veligers from those of quagga and zebra mussels, as this distinction is necessary for targeted prevention programs. Microscopy, a primary tool for early detection monitoring, is used to conduct morphological comparisons between the veligers of these species to assess whether visual differentiation is possible.
While large-scale chemical decontamination for watercraft has not been implemented in mussel management programs in the West, there remains a need for chemical treatment options for field equipment, so another priority is efficacy studies on approved chemicals targeting golden mussels. The Department of Water Resources (DWR) is conducting chemical toxicity studies to support the maintenance of its water infrastructure. Additionally, DWR has provided golden mussel adults to the Smithsonian Institute, which is studying their salinity tolerances to further inform management and prevention strategies.
“There’s much interest in golden mussels and so many unanswered questions relative to their presence in North America,” said Ms. Volkoff. “Those research questions have been identified in the hopes that we can match researchers up or others that can pursue work on that, to move all of our efforts, not just in California but nationally, forward.”
DISCUSSION
Chair Inge Werner asked about the need to set standards. Hasn’t that been done for zebra and quagga mussels already?
“The western states have made great progress over the last 18 years around quagga and zebra mussels,” said Ms. Volkoff. “There are documents that have been developed and vetted through Western states. They are available as the foundation for setting standards in California. What is different in California than in many Western states is that water management and access to water are not under state management. In California, we have an array of local agencies responsible for managing water and access to those waters. So, the state of California, unless it compelled or mandated all of those local agencies to conform to a standard, we do not have the authority to set one standard. So what we are envisioning is developing a voluntary standard that others can opt into participating in but we cannot compel them to.”
Dr. Jayanta Obeysekera noted the absence of any modeling of projections or scenarios about how fast golden mussels could grow because, at some point, without knowing that your protection measures might not be adequate, the spread might outpace the protection measures.
“Based on the information we have, at least in the State Water Project and looking at flows of water, I think all you need to do is look at the flow of water, and that is the footprint of golden mussels today,” said Ms. Volkoff. “They have been detected incrementally in the State Water Project, and where there’s opportunity to inspect, I expect many more dots on the map this summer. I don’t think we could model fast enough to keep up with the mussels. That was the experience back in 2007 for quagga and zebra mussels in the Colorado River Aqueduct; when there was the detection in Lake Mead, Southern California immediately started looking through their water distribution, and they were there. They were already present in the system.”
“Our best opportunity is the overland transport and protecting those nonconnected waters of California … it’s the smaller water agencies and water distribution systems. There’s a lot to protect there, and it’s addressing the vectors for open land spread.“
“With the reality of limited resources, you have to choose between investing in research to benefit others or trying to implement prevention of spread,“ she continued. “Unless there are researchers who come in, it is not our immediate priority to do the research. There are many interesting research questions that would benefit others, but I don’t have the capacity in my program to devote staff and time to that when we’re trying to equip water managers to prevent introductions. I have to place our resources there. I am really interested in that, and maybe through your channels and communities, you have a network of scientists who could devote the attention to this in terms of growth rates and predicting what the future will look like in the Delta.”
Ms. Volkoff recalled the Chinese mitten crab invasion, where there was a phenomenal boom and then bust in the population. “There really wasn’t research to my knowledge to explain or try to explain why that bust happened. And someone asked me, is it possible that will happen with golden mussels in the Delta? And while I would like to hope that might be a possibility, I anticipate, because of such a productive system, that is unlikely. But I can hold out hope. But again, from the agency perspective, we’re limited and constrained by our available resources.”
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