Title
Summary of the Invasive Mussel Prevention Program activities at the Nacimiento and San Antonio Reservoirs.
Report
SUMMARY/DISCUSSION:
Quagga and Zebra mussels were first introduced to California in 2008. In response, the Agency, Monterey County Parks and SLO County Flood Control and Water Conservation District began the implementation of a Mussel Prevention Program at Nacimiento and San Antonio Reservoirs. In 2024, a new invasive mussel, the Golden Mussel was detected in the San Joaquin Delta. Compared to previous invasive mussels, Golden Mussels have a higher tolerance for a range of environmental conditions such as salinity and water temperature.
These invasive mussels pose a threat to water infrastructure, ecosystem and economy. Mussels can clog water intake pipes, dam operation infrastructure, and powerplant equipment, as well as threaten downstream infrastructure. Invasive mussels are also harmful to the environment, causing an increase in harmful algal blooms and consuming material that the native and sport fish populations rely on. In terms of recreation, invasive mussels can foul watercraft motors, docks, and boat launches. The biggest threat to getting invasive mussels comes from watercraft and equipment coming from other water bodies that are infested.
Updates to the Invasive Mussel Prevention Program
Since the detection of golden mussels in California, the Agency has increased collaboration with our partners, Monterey County Parks and SLO County Flood Control and Water Conservation District. Additional precautions have been added to the Invasive Mussel Prevention Program standards that were implemented at the beginning of 2025. These changes include creating and disturbing new inspector stamps and removing old stamps from rotation to ensure that all inspectors are recently certified, incorporating the Watercraft Inspections and Decontamination (WID) system with all inspectors including private ramps, and creating separate bands for San Antonio and Nacimiento requiring an additional inspection when going in between reservoirs.
Grant funding
In August 2025, the Agency was awarded grant funding from CDFW to support the Invasive Mussel Prevention program. With funding from this grant, six Agency staff members completed the level one training and certification for Watercraft Inspection and Decontamination of Invasive Species. Starting in summer 2026, funds will be used to retain mussel detection canines on busy boating weekends. In collaboration with Monterey County Parks, funding from this grant will also be going towards equipment purchases to ensure that vessel inspectors at public launch ramps have robust access to the Watercraft Inspections and Decontamination (WID) system at both reservoirs and towards the enhancement of public boat launch ramp facilities at Nacimiento Reservoir to make them more secure.
Next Steps
The Agency is currently working to complete the San Antonio Prevention Plan and receive approval from CDFW. The agency is looking for additional grant funding opportunities to support the completion of this plan and additional support for enforcement at the reservoirs. The agency is also having conversations with CDFW for their support as needed.
OTHER AGENCY INVOLVEMENT:
None
FINANCING:
CDFW 2025 Mussel Prevention and Boating Access Grant and Fund 111 (1501).
Prepared by: Marinn Browne, Biologist, (831) 788-3450