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Lake Oroville Community Update
May 22, 2025
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Golden Mussels Found During Boat Inspection at Thermalito Forebay
Ongoing Watercraft Inspections Aim to Prevent the Spread of Invasive Mussels
The Department of Water Resources’ (DWR) newly implemented invasive mussel inspection program for State Water Project (SWP) facilities in Oroville uncovered golden mussels attached to a pontoon boat late Wednesday afternoon in Butte County. Staff immediately contacted the California Department of Fish and Wildlife (CDFW) for further inspection and decontamination. The vessel will not be allowed to launch at a DWR reservoir until CDFW confirms that it is free of mussels.
The pontoon had been out of the Delta waters for an unknown period and was purchased Wednesday morning in Stockton by Oroville-area residents who planned to launch the boat at Lake Oroville for the Memorial Day weekend. The boat was brought to DWR’s inspection site at the North Thermalito Forebay where golden mussels ranging in size from approximately 1/8 inch to 3/4 inch were discovered during the inspection.
“We are thankful that DWR’s new inspection program in Oroville caught these highly destructive mussels before they could be introduced to our largest water supply reservoir,” said John Yarbrough, DWR’s Deputy Director of the State Water Project. “Oroville’s reservoirs provide water to the Feather River Fish Hatchery and several municipal water agencies for residential, business, and agricultural use, produce hydroelectric power, and provide flood control. Yesterday’s discovery further highlights the importance of protecting these critical functions through watercraft inspections given the ease with which golden mussels are transported from the Delta.”
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DWR launched its mandatory invasive mussel inspection program for the Oroville facilities – Lake Oroville, Thermalito Forebay, and Thermalito Afterbay – on Monday, May 19, with voluntary inspections beginning Friday, May 16. Since May 16, DWR’s Oroville program has inspected and sealed over 875 watercraft and decontaminated approximately 215 vessels before Memorial Day, one of the most popular holidays for outdoor recreating. Inspection and vessel decontamination services are free.
Golden mussels were first discovered in the Port of Stockton in October 2024. That same month, golden mussels were discovered at the SWP’s O’Neill Forebay in Merced County.
Adult golden mussels range from ¾ inches to 2 inches in size and have a light to dark yellowish-brown to brown-colored shell. When golden mussel populations are established, they are difficult to control due to their rapid growth and are easily spread to new waterbodies. Golden mussels can alter aquatic ecosystems by filter-feeding on planktonic algae and changing the habitat structure, which can damage fisheries, impact water delivery systems by clogging small-diameter pipelines, screens, and filters, and impact recreation by fouling boat hulls and motors and clogging intakes and cooling lines. Mussel larvae, also referred to as veligers, are microscopic and free floating in infested waters, and can be transported in a boat’s live well, ballast tank, or in the bilge if these areas are not completely drained.
DWR is reminding watercraft owners to clean, drain, and dry to prevent the spread of invasive mussels in California’s waterways. More information about DWR’s Oroville mussel inspection program is available at water.ca.gov/mussels.
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California Department of Water Resources
715 P Street
Sacramento, CA 95814
Call our general information line at 916-820-8142
or email us at oroville@water.ca.gov
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