Golden Mussel & Aquatic Invasive Species (AIS) Information

Golden Mussel & Aquatic Invasive Species Information

Tri-Dam Project is actively working to prevent the introduction and spread of aquatic invasive species, including the Golden Mussel. The invasive Golden mussel (Limnoperna fortunei), a non-native freshwater/brackish bivalve, has been detected in the Sacramento - San Joaquin Delta - the first known occurrence of golden mussels in North America.

The species poses a significant immediate threat to the natural ecosystems, water infrastructure and water quality.

Golden mussels can spread quickly between water bodies by attaching to boats, trailers, and equipment. Once established, they can impact water infrastructure, ecosystems, and recreation.

At this time:

• No golden mussels have been detected at Tulloch Reservoir
• No golden mussels have been detected at Beardsley or Donnells Reservoir

Preventative measures help keep our reservoirs open and protected.

Example Photos of Invasive Mussels Observed in California

Educational Photo Examples:
The following photos were taken in areas of the San Joaquin Delta where invasive mussels have been observed. These images are provided for educational purposes. Golden mussels have not been detected at Tulloch or Beardsley Reservoir.

A person is holding a barnacle-covered object above a wooden dock, revealing marine growth on the surface.

Example of mussel colonization on infrastructure observed in the Sacramento–San Joaquin Delta. Golden mussels have not been detected at Tulloch or Beardsley Reservoir.

A hand in a green glove holding several dark, slimy objects, possibly aquatic creatures or debris.

Close-up example of invasive mussels collected from areas where the species has been detected in California.

A hand points at a round, slightly dirty buoy near a wooden dock, with a foot in a sandal visible in the foreground.

These mussels attach to hard surfaces such as boats, docks, pipes, and water infrastructure, forming dense colonies that can damage facilities.

RESERVOIR	OPERATIONAL STATUS	BOATING REQUIREMENTS
Tulloch	Operating under the same AIS prevention protocols as last season	Launching available only through authorized facilities; AIS inspection and banding requirements apply
Beardsley	Operating under the same conditions as the previous season	Public boat launching remains closed at this time
Donnells	Reservoir operations ongoing	No developed boat launch. Limited access for small watercraft via hike-in areas; visitors should complete a self-inspection prior to launching

Tri-Dam continues to operate under the same Aquatic Invasive Species (AIS) prevention protocols that were in place last season. Visitors should check current access requirements before planning a trip to the reservoir.

Why Prevention Measures Are Important

Example of invasive mussels attached to the underside of a boat hull. — Example of invasive mussels attached to the underside of a boat in the Sacramento–San Joaquin Delta. Mussels can attach to boats, trailers, and equipment and be transported between water bodies if vessels are not properly cleaned. Golden mussels have not been detected at Tri-Dam Reservoirs.

Aquatic invasive species can:

• Clog water infrastructure
• Damage ecosystems and fisheries
• Spread rapidly between lakes and reservoirs
• Require costly long-term management

Prevention is the most effective way to protect California waterways.

Where can Golden Mussels live?

Golden mussel can inhabit fresh and brackish-water lakes, rivers, creeks, wetlands, bays, and canals with water temperatures ranging from 41-95°F. They can establish in waters with a constant salinity of less than 3 parts per thousand (ppt) and can survive fluctuations of higher salinities. They attach to a wide variety of substrates, both man-made and natural, and at various water depths. Golden mussels are not restricted to hard surfaces and have been found colonizing soft substrates and attached to aquatic plants.

How does the Golden Mussel impact the environment?

Golden mussels are highly efficient filter feeders and form dense colonies. They consume large quantities of aquatic microscopic plants and animals that native species and sport fish depend on for food. Their colonization of hard surfaces impedes water flow, clogs pipes, and fouls watercraft motors, and necessitates ongoing, costly removal to maintain operational function. These costs result in economic impacts to water conveyances, energy production, recreation, agriculture, and ultimately the public.

Boating Requirements at Tulloch Reservoir

To help prevent the spread of invasive species:

• Boats must launch from authorized facilities
• Vessels may be subject to inspection
• Approved banding programs may be required
• Boats must be Clean, Drained, and Dry
• Non-motorized watercraft users may be required to complete a Self-Inspection Permit prior to launching

Download the self-inspection form here: Mussel Self-Inspection Permit

These measures helps reduce the risk of introducing Golden Mussels and other aquatic nuisance species by confirming that watercraft and equipment have been properly cleaned, drained, and dried.

What You Can Do

All boaters can help prevent the spread of invasive species by following these steps:

The image promotes a message to not move mussels in California, featuring golden, quagga, and zebra mussels, with a call to clean, drain, and dry.

Clean – Remove plants, mud, and debris from boats and trailers
Drain – Drain all water from boats and equipment
Dry – Allow boats and equipment to dry before launching in another water body

How do I report Golden Mussel sightings?

If you observe golden mussel in California immediately report your sighting to the CDFW Invasive Species Program, or by email to Invasives@wildlife.ca.gov, or by telephone to 866-440-9530. Please take clear, close-up photos that include something (such as a pencil or hand) to show size.

Learn More

Additional information about reservoir operations and AIS prevention programs can be found on the following • AIS Program Information

• Mussel Self-Inspection Permit

• Frequently Asked Questions