Invasive Golden Mussels Confirmed in Silverwood, Pyramid Lakes

Detection and spread: how the mussels reached Southern California

State officials confirmed golden mussels at Silverwood Lake and Pyramid Lake in September 2025. These are the southernmost confirmed infestations in the State Water Project system so far. Initial California reports came from the Sacramento–San Joaquin Delta and O’Neill Forebay in October 2024, and the mussels have moved more than 300 miles within the state in less than a year.

Read the California Department of Water Resources news release for official details and timelines.

How they spread

Golden mussels are native to China and Southeast Asia. They spread quickly because microscopic larvae called veligers drift in the water and microscopic eggs or adults can hitch rides on boats, trailers and gear. Veligers can survive in small amounts of water left in cooling systems, live wells or bilges — making boats a major pathway.

Boaters are a critical link: removing water and cleaning gear reduces the risk of moving veligers between waterbodies.

Ecological and infrastructure threats

Golden mussels attach to hard surfaces and form dense colonies that can:

• Clog water delivery systems, pumps, screens and intake pipes — threatening municipal and agricultural water supplies.
• Outcompete native mussels and aquatic animals, altering food webs and potentially reducing fish populations.
• Change water clarity and nutrient cycles, which can promote harmful algal blooms and impair water quality and public health.
• Attach to hulls, motors and intake screens, damaging boats and reducing recreational value — increasing maintenance costs for owners and marinas.

“Once golden mussels are established in a lake, there is no reliable method to remove them entirely.” — experts urge early detection and prevention.

Current management and control steps

State agencies including the California Department of Water Resources (DWR) news release, Keep Tahoe Blue partners and local water agencies are coordinating monitoring, inspections and public notices at affected reservoirs.

Inspection protocols

Silverwood Lake: Entry inspections have ended because the lake is now classed as infested. Managers require exit inspections: all boats leaving must have drain plugs removed; boaters are strongly advised to clean, drain and dry vessels before visiting other water bodies.

Pyramid Lake: Continues exit inspections under policies used during earlier quagga mussel responses.

Lake Perris — downstream and receiving daily transfers from Silverwood — is considered high risk. Inspections there remain in place; managers may change to exit-only protocols if mussels are detected.

Expanded surveillance and suspected reports

Agencies are increasing surveillance in other reservoirs and in the Bay-Delta. Suspected or single detections have been reported at Lake Oroville, in Butte County waters and at Clear Lake, prompting targeted containment efforts and local advisories.

See reporting from the U.S. Forest Service and local news coverage for latest alerts.

How golden mussels spread — and what the public can do

Mussels most often spread on boats, trailers and gear. Even small amounts of water left in a bilge, live well or engine can carry veligers. Weeds, anchors, ropes and dive gear can also move mussels between lakes.

Follow “Clean, Drain, Dry” every time:

• Clean off visible plants, animals and mud.
• Drain all water from boats, motors, live wells and gear.
• Dry everything for several days before visiting another water body.

Report unusual shells, sticky clusters on equipment, or tiny veligers to California Department of Fish and Wildlife (CDFW) and local park staff to help managers track spread and respond faster.

Implications for The Inland Empire

Economic impact

The Inland Empire relies on Silverwood Lake for recreation, local water storage and parts of the State Water Project. Clogged intakes and damaged pumps could raise costs for water agencies and farmers, and increase repair bills for boat owners and marinas. Tourism tied to boating and fishing at Silverwood and nearby Lake Perris could suffer if infestations spread.

Political and social effects

County and city leaders are likely to face pressure to secure supply and protect infrastructure. Local agencies may request more state and federal funds for monitoring and mitigation. Recreational users will encounter new rules and inspections; boat owners may face added cleaning and maintenance costs. Clear communication and outreach will be essential to limit confusion.

Cultural relevance

Lakes in the Inland Empire are long-held community assets. Threats to water quality and access can affect family outings, fishing tournaments and youth programs. Protecting these places will likely become a shared local priority across political lines.

Practical actions for residents

• Follow exit inspection rules at Silverwood and Pyramid: remove drain plugs before leaving; clean, drain and dry gear.
• Avoid moving boats or gear between infested and uninfested waters until cleared by authorities.
• Report sightings to CDFW and park authorities; heed posted advisories.
• Watch for agency updates about inspections at Lake Perris and nearby reservoirs — policies may change quickly to prevent spread.

Sources and further reading

• California Department of Water Resources news release: Invasive Golden Mussel Detected at Silverwood Lake and Pyramid Lake
• Keep Tahoe Blue: Golden mussels too close for comfort
• Contra Costa Water District: Golden Mussels
• U.S. Forest Service: Help halt mussel invasion
• KRCRTV reporting on suspected detections
• Lake County official advisory on mussel detection efforts

Reporting by Times Media Service